HH 8 Chuan KTKN

Chng I : T GIAC

TUAN I

Chng I : T GIAC

Tiet 1: 1. T giac *****I/ MUC TIEU :- HS nam vng cac nh ngha ve t giac, t giac loi, tong cac goc cua t giac loi.

- HS biet ve, biet goi ten cac yeu to, biet tnh so o cac goc cua mot t giac loi. Biet van dung cac kien thc trong bai vao cac tnh huong thc tien n gian.

- Suy luan ra c tong bon goc ngoai cua t giac bang 360o.

II/ CHUAN B :- GV : Compa, eke, thc thang, bang phu ve hnh san (H1, H5 sgk)

- HS : On nh l tong so o cac goc trong tam giac. III/ PHNG PHAP:

am thoai, qui nap, hoat ong nhom.

III/ HOAT ONG DAY- HOC :NOI DUNG HOAT ONG CUA GV HOAT ONG CUA HS

Hoat ong 1 : Kiem ra (5)

- Kiem tra o dung hoc tap cua HS, nhac nh HS cha co u - HS cung ban kiem tra lan nhau va bao cao

Hoat ong 2 : Gii thieu bai mi (1)

1. T GIAC- Gii thieu tong quat kien thc lp 8, chng I, bai mi - HS nghe va ghi ten chng, bai vao v.

Hoat ong 3 : nh ngha (20)

1.nh ngha:

+T giac ABCD la hnh gom 4 oan thang AB, BC, CD, DA, trong o bat ky 2 oan thang nao cung khong cung nam tren 1 ng thang

T giac ABCD (hay ADCB, BCDA, )

- Cac nh: A, B, C, D

- Cac canh: AB, BC, CD, DA.+T giac loi la t giac luon

nam trong 1 na mat phang co b la ng thang cha bat ky canh nao cua t giac

?2

- Treo hnh 1,2 (sgk) : Moi hnh tren eu gom 4 oan thang AB, BA, CD, DA. Hnh nao co hai oan thang cung thuoc mot ng thang?

- Cac hnh 1a,b,c eu c goi la t giac, hnh 2 khong c goi la t giac. Vay theo em, the nao la t giac ?

- GV chot lai (nh ngha nh SGK) va ghi bang

- GV giai thch ro noi dung nh ngha bon oan thang lien tiep, khep kn, khong cung tren mot ng thang

- Gii thieu cac yeu to, cach goi ten t giac.

- Thc hien ?1 : at mep thc ke len moi canh cua t giac hnh a, b, c roi y/c HS tra li ?1

- GV chot lai van e va neu nh ngha t giac loi

- GV neu va giai thch chu y (sgk)

- Treo bang phu hnh 3. yeu cau HS chia nhom lam ?2- GV quan sat nhac nh HS khong tap trung

- ai dien nhom trnh bay

- HS quan sat va tra li

(Hnh 2 co hai oan thang BC va CD cung nam tren mot oan thang)

- HS suy ngh tra li

- HS1: (tra li)

- HS2: (tra li)

- HS nhac lai (vai lan) va ghi vao v

- HS chu y nghe va quan sat hnh ve e khac sau kien thc

- Ve hnh va ghi chu vao v

- Tra li: hnh a

- HS nghe hieu va nhac lai nh ngha t giac loi

- HS nghe hieu

- HS chia 4 nhom lam tren bang phu

- Thi gian 5

a)* nh ke: A va B, B va C, C va D, D va A

* nh oi nhau: B va D, A va Cb) ng cheo: BD, AC

c) Canh ke: AB va BC, BC va CD,CD va DA, DA va AB

d) Goc: A, B, C, D

Goc oi nhau: A va C, B va D

e) iem nam trong: M, P iem nam ngoai: N, Q

Hoat ong 4 : Tong cac goc cua mot t giac (7)

2. Tong cac goc cua mot t giac

Ke ng cheo AC, ta co :

A1 + B + C1 = 180o,

A2 + D + C2 = 180o

(A1+A2)+B+(C1+C2)+D = 360o

vay A + B + C + D = 360o

nh l : (Sgk)

- Ve t giac ABCD :D oan xem tong so o bon goc cua t giac bang bao nhieu?

- Cho HS thc hien ?3 theo nhom nho

- Theo doi, giup cac nhom lam bai

- Cho ai dien vai nhom bao cao

- GV chot lai van e (neu phng hng va cach lam, roi trnh bay cu the) - HS suy ngh (khong can tra li ngay)

- HS thao luan nhom theo yeu cau cua GV

- ai dien mot vai nhom neu ro cach lam va cho biet ket qua, con lai nhan xet bo sung, gop y

- HS theo doi ghi chep

- Neu ket luan (nh l) , HS khac lap lai vai lan.

Hoat ong 5 : Cung co (7)

Bai 1 trang 66 Sgk

a) x=500 (hnh 5)b) x=900

c) x=1150

d) x=750

a) x=1000 (hnh 6)

a) x=360- Treo tranh ve 6 t giac nh hnh 5, 6 (sgk) y/c HS nham tnh

va tra li ket qua.

- HS tnh nham so o goc x

a) x=500 (hnh 5)

b) x=900

c) x=1150

d) x=750

a) x=1000 (hnh 6)

a) x=360

Hoat ong 6 : Dan do (5)

BTVN.Bai tap 2 trang 66 Sgk

Bai tap 3 trang 67 Sgk


Bai tap 5 trang 67 Sgk- Hoc bai: Nam s khac nhau gia t giac va t giac loi; t chng minh nh l tong cac goc trong t giac

- Bai tap 2 trang 66 Sgk! S dung tong cac goc 1 t giac

- Bai tap 3 trang 67 Sgk

! Tng t bai 2- Bai tap 4 trang 67 Sgk

! S dung cach ve tam giac

- Bai tap 5 trang 67 Sgk! S dung toa o e tm- HS nghe dan va ghi chu vao v

Tiet 2: 2. Hnh thang *****I/ MUC TIEU :

- HS nam c nh nghia hnh thang, hnh thang vuong, cac yeu to cua hnh thang. Biet cach chng minh mot t giac la hnh thang, la hnh thang vuong.

- HS biet ve hnh thang, hnh thang vuong; tnh so o cac goc cua hnh thang, hnh thang vuong. Biet s dung dung cu e kiem tra mot t giac la hnh thang.

- Biet linh hoat khi nhan dang hnh thang nhng v tr khac nhau va cac dang ac biet (hai canh song song, hai ay bang nhau)

II/ CHUAN B :

- GV : Thc thang, eke, bang phu ( ghi cau hoi ktra, ve san hnh 13), phan mau- HS : Hoc va lam bai nha; v ghi, sgk, thc, eke

III/ PHNG PHAP:

-am thoai, qui nap, hp tac nhom

IV/ HOAT ONG DAY- HOC :

NOI DUNG HOAT ONG CUA GV HOAT ONG CUA HS

Hoat ong 1 : Kiem ra bai cu (8)

- nh ngha t giac ABCD?

- l ve tong cac goc cua mot t giac?

- Cho t giac ABCD,biet

= 65o, = 117o, = 71o

+ Tnh goc D?

+ So o goc ngoai tai D? - Treo bang phu ghi cau hoi kiem tra; goi mot HS len bang.

- Kiem tra v btvn vai HS

- Thu 2 bai lam cua HS

- anh gia, cho iem

- Chot lai cac noi dung chnh (nh ngha, l, cach tnh goc ngoai)- Mot HS len bang tra li va lam bai len bang. Ca lp lam bai vao v .

= 3600-650-1170-710= 1070

Goc ngoai tai D bang 730

- Nhan xet bai lam bang .

- HS nghe va ghi nh


2. HNH THANG

- Chung ta a biet ve t giac va tnh chat chung cua no. T tiet hoc nay, chung ta se nghien cu ve cac t giac ac biet vi nhng tnh chat cua no. T giac au tien la hnh thang. - HS nghe gii thieu

- Ghi ta bai vao v

Hoat ong 3 : Hnh thanh nh ngha (18)

1.nh ngha: (Sgk)

Hnh thang ABCD (AB//CD)

AB, CD : canh ay

AD, BC : canh ben

AH : ng cao

* Hai goc ke mot canh ben cua hnh thang th bu nhau.

* Nhan xet: (sgk trang 70)

- Treo bang phu ve hnh 13: Hai canh oi AB va CD co g ac biet?

- Ta goi t giac nay la hnh thang. Vay hnh thang la hnh nh the nao?

- GV neu lai nh nghia hnh thang va ten goi cac canh.

- Treo bang phu ve hnh 15, cho HS lam bai tap ?1

- Nhan xet chung va chot lai ve

- Cho HS lam ?2 (ve san cac hnh 16, 17 sgk)

- Cho HS nhan xet bang

- T b.tap tren hay neu ket luan?

- GV chot lai va ghi bang - HS quan sat hnh , neu nhan xet AB//CD

- HS neu nh ngha hnh thang

- HS nhac lai, ve hnh va ghi vao v

- HS lam ?1 tai cho tng cau

- HS khac nhan xet bo sung

- Ghi nhan xet vao v

- HS thc hien ?2 tren phieu hoc tap hai HS lam bang

- HS khac nhan xet bai

- HS neu ket luan

- HS ghi bai

Hoat ong 4: Hnh thang vuong (8)

2.Hnh thang vuong:

A B

D C

Hnh thang vuong la hnh thang co 1 goc vuongCho HS quan sat hnh 18, tnh ?

Noi: ABCD la hnh thang vuong. Vay the nao la hnh thang vuong?

- HS quan sat hnh tnh

= 900- HS neu nh ngha hnh thang vuong, ve hnh vao v

Hoat ong 5: Cung co (5)

Bai 7 trang 71a) x = 100o ; y = 140o

b) x = 70o ; y = 50o

c) x = 90o ; y = 115o - Treo bang phu hnh ve 21 (Sgk)

- Goi HS tra li tai cho tng trng hp- HS kiem tra bang trc quan, bang e ke va tra li

- HS tra li mieng tai cho bai tap 7

Hoat ong 6: Dan do (5)




Bai tap 10 trang 71 Sgk- Hoc bai: thuoc nh ngha hnh thang, hnh thang vuong.

- Bai tap 6 trang 70 Sgk- Bai tap 8 trang 71 Sgk! +++ = 360o

- Bai tap 9 trang 71 Sgk! S dung tam giac can

- Bai tap 10 trang 71 Sgk-Chuan b : thc co chia khoang, thc o goc, xem trc 3- HS nghe dan va ghi chu

- Xem lai bai tam giac can

- em so hnh thang

To duyet

BGH duyet

TUAN II

Tiet 3: 3. Hnh thang can *****I/ MUC TIEU:

- HS nam vng nh ngha, cac tnh chat, cac dau hieu nhan biet hnh thang can.

- HS biet ve hnh thang can, biet s dung nh ngha va tnh chat cua hnh thang can trong tnh toan va chng minh, biet chng minh t giac la hnh thang can.

II/ CHUAN B :- GV : Thc chia khoang, thc o goc, compa; bang phu

- HS : Hoc bai cu, lam bai nha; dung cu: thc chia khoang thc o goc

III/ PHNG PHAP:

- Van ap, neu van e.

III/ HOAT ONG DAY- HOC :



1- nh ngha hnh thang (neu ro cac yeu to cua no) (4)

2- Cho ABCD la hnh thang (ay la AB va CD) Tnh xvay (6) - Treo bang phu - Goi mot HS len bang

- Kiem btvn vai HS

- Cho HS nhan xet

- Nhan xet anh gia va cho iem - HS lam theo yeu cau cua GV:

- Mot HS len bang tra li

x =1800 - 110= 700

y =1800 - 110= 700

- HS nhan xet bai lam cua ban

- HS ghi nh , t sa sai (neu co)


3 HNH THANG CAN- tiet trc (GV nhac lai)

- tiet nay chung ta se nghien cu ve dang ac biet cua no - Chuan b tam the vao bai mi

- Ghi ta bai


1.nh ngha:

Hnh thang can la hnh thang co 2 goc ke 1 ay bang nhauT giac ABCD laHnh thang can (ay AB, CD)

- Co nhan xet g ve hnh thang tren (trong e ktra)?

- Mot hnh thang nh vay goi la hnh thang can. Vay hnh thang can la hnh nh the nao?

- GV tom tat y kien va ghi bang

- GV: Thong bao chu y SGK.- a ra ?2 tren bang phu

- GV chot lai bang cach ch tren hnh ve va giai thch tng trng hp

- Qua ba hnh thang can tren, co nhan xet chung la g? - HS quan sat hnh va tra li (hai goc ay bang nhau)

- HS suy ngh, phat bieu

- HS phat bieu lai nh ngha

- HS: Lang nghe- HS suy ngh va tra li tai cho

- HS khac nhan xet

- Tng t cho cau b, c

- Quan sat, nghe giang

-HS neu nhan xet: hnh thang can co hai goc oi bu nhau.

Hoat ong 4 : Tm tnh chat canh ben (12)

2.Tnh chat :

a) nh l 1:

Trong hnh thang can , hai canh ben bang nhau O

A B

D C

GT ABCD la hnh thang

(AB//CD)

KL AD = BC

Chng minh: (sgk trang 73)

Chu y : (sgk trang 73)- Cho HS o cac canh ben cua ba hnh thang can hnh 24

- Co the ket luan g?

- Ta chng minh ieu o ?

- GV ve hnh, cho HS ghi GT, KL

- Trng hp canh ben AD va BC khong song song, keo dai cho chung cat nhau tai O cac (ODC va OAB la tam giac g?

- Thu vai phieu hoc tap, cho HS nhan xet bang

- Trng hp AD//BC ?

- GV: Hnh thang co hai canh ben song song th hai canh ben bang nhau. Ngc lai, hnh thang co hai canh ben bang nhau co phai la hnh thang can khong?

- Treo hnh 27 va neu chu y (sgk)- Moi HS t o va nhan xet.

- HS neu nh l

- HS suy ngh, tm cach c/minh

- HS ve hnh, ghi GT-KL

- HS nghe gi y

- Mot HS len bang chng minh trng hp a, ca lp lam vao phieu hoc tap

- HS nhan xet bai lam tren bang

- HS suy ngh tra li

- HS suy ngh tra li

- HS ghi chu y vao v

b) nh l 2:

Trong hnh thang can, hai ng cheo bang nhau

GT ABCD la hthang can

(AB//CD)

KL AC = BD

Cm: (sgk trang73)- Treo bang phu (hnh 23sgk)

- Theo nh l 1, hnh thang can ABCD co hai oan thang nao bang nhau ?

- D oan nh the nao ve hai ng cheo AC va BD?

- Ta phai cminh nh lsau

- Ve hai ng cheo, ghi GT-KL?

- Em nao co the chng minh ?

- GV chot lai va ghi bang- HS quan sat hnh ve tren bang

- HS tra li (ABCD la hnh thang can, theo nh l 1 ta co AD = BC)

- HS neu d oan (AC = BD)

- HS o trc tiep 2 oan AC, BD

- HS ve hnh va ghi GT-KL

- HS trnh bay mieng tai cho

- HS ghi vao v

Hoat ong 5 : Tm dau hieu nhan biet hnh thang can (6)

3. Dau hieu nhan biet hnh thang can:

a) nh L 3: Sgk trang 74

b) Dau hieu nhan biet hnh thang can :

1. Hnh thang co goc ke mot ay bang nhau la hnh thang can

2. Hnh thang co hai ng cheo bang nhau la hthang can - GV cho HS lam ?3

- Lam the nao e ve c 2 iem A, B thuoc m sao cho ABCD la hnh thang co hai ng cheo AC = BD? (gi y: dung compa)

- Cho HS nhan xet va chot lai:

+ Cach ve A, B thoa man k

+ Phat bieu nh l 3 va ghi bang

- Dau hieu nhan biet hthang can?

- GV chot lai, ghi bang- HS oc yeu cau cua ?3

- Moi em lam viec theo yeu cau cua GV:

+ Ve hai iem A, B

+ o hai goc C va D

+ Nhan xet ve hnh dang cua hnh thang ABCD.

-HS phat bieu

- HS nhac lai va ghi bai


BTVN.- Bai tap 12 trang 74 Sgk


- Bai tap 15 trang 75 Sgk- Hoc bai : thuoc nh ngha, cac tnh chat , dau hieu nhan biet


Ap dung: Cac trng hp bang nhau cua tam giac.

- Bai tap 13 trang 74 SgkTnh chat hai ng cheo hnh thang can va phng phap chng minh tam giac can

- Bai tap 15 trang 75 Sgk- HS nghe dan

- HS ghi chu vao tap

Tiet 4: Luyen tap 3 *****I/ MUC TIEU:- Hoc sinh c cung co va hoan thien ly thuyet: nh ngha, tnh chat hnh thang can, cac dau hieu nhan biet mot hnh thang can .

- HS biet van dung cac tnh chat cua hnh thang can e giai mot so bai tap tong hp; ren luyen ky nang nhan biet hnh thang can .

- Ren luyen cac thao tac phan tch, tong hp, xac nh hng chng minh mot bai toan hnh hoc.

II/ CHUAN B :- GV : Bang phu ghi e kiem tra, bai tap .

- HS : Hoc bai va lam cac bai tap a cho va a c hng dan

III/ PHNG PHAP: - am thoai, gi m, hp tac nhom



Hoat ong 1 : Kiem tra bai cu (12)

Bai 15 trang 75 Sgk

Giai

a) = (180o-A) :2

( DE // BC.

Hnh thang BDEC co nen la hnh thang can.

b) =(1800-500) :2 = 650 = (3600-1300) :2= 1150 - Cho HS sa bai 15 (trang 75)

- GV kiem bai lam nha cua mot vai HS


- anh gia; khang nh nhng cho lam ung; sa lai nhng cho sai cua HS va yeu cau HS nhac lai cach c/m 1 t giac la hthang can

- Qua bai tap, rut ra mot cach ve hnh thang can? - Mot HS ve hnh; ghi GT-KL trnh bay li giai

- Ca lp theo doi

- HS neu y kien nhan xet, gop y bai lam tren bang

- HS sa bai vao v

- HS nhac lai cach chng minh hnh thang can

- HS neu cach ve hnh thang can t mot tam giac can

Hoat ong 2 : Luyen tap (28)

Bai tap 16 SGK tr 75:

A

E D

B C

can tai A

GT DB la ng phan giac.

CE la ng phan giac.

KL BEDC la hnh thang can

EB = ED.

CM.

Tam giac ABC can

nen =

Suy ra: =

Hai tam giac ABD va ACD co: = .

AB = AC.

chung.

Nen: (c.g.c)

( AD = AE.

( can.

=.

Mat khac:

=

Vay =

( ED // BC

( BCDE la hnh thang.

va =

Nen BCDE la hnh thang can.

Ta lai co: = v ED // BC

= (BD la pg)

Vay =

( can tai E.

( EB = ED

Bai 17 trang 75 Sgk

GT hthang ABCD (AB//CD)

KL ABCD can

Giai

Goi O la giao iem cua AC va BD, ta co:

Ta co: AB// CD (gt)

Nen: ( sletrong)

( soletrong)

Do o (OAB can tai O

( OA = OB (1)

Lai co (gt)

OC = OD (2) T (1) va (2) ( AC = BD

Cho HS thc hien Bai tap 16 SGK.

- Yeu cau HS oc e, ve hnh va ghi gia thiet, ket luan.

- Hng dan hoc sinh thc hien tng bc.

?. e chng minh DEDC la hnh thang can ta phai chng minh g?

_Ta can CM AE = AD vay e bai tap tr ve bt 15a/

_ay nho la oan nao?

_Canh ben la oan nao?

_CM g?

_Neu DE = BC th (BED the nao?

V sao?

_GV s lc lai phng phap giai va yeu cau HS xung phong len bang.

_GV chu y nhan xet sa sai ngay neu co bang.

_GV nhan xet, sa cha.

-Cho HS oc e bai, GV ve hnh len bang, goi HS tom tat gt-kl

- Chng minh ABCD la hnh thang can nh the nao?

- Vi ieu kien , ta co the chng minh c g? =>

- Can chng minh them g na?

=> ?

- T o => ?

- Goi 1 HS giai; HS khac lam vao nhap


- GV hoan chnh bai cho HS

HS oc e va ve hnh bang.

_DE

_BE hoac CD

_DE = BC

_(BED can tai E -> =

_HS tra li.

_HS chu y GV s lc va xung phong len bang.

_Cac HS khac chu y bang _HS khac nhan xet.

- HS oc e bai, ve hnh va tom tat Gt-Kl.

- Hnh thang ABCD co

AC=BD

(ODC can

=> OD=OC

- Can chng minh (OAB can

=> OA=OB

AC=BD

Goi O la giao iem cua AC va BD, ta co:

Ta co: AB// CD (gt)

Nen: (soletrong)

( soletrong)

Do o (OAB can tai O

( OA = OB (1)

Lai co (gt)

OC = OD (2)

T (1) va (2) ( AC = BD

- Nhan xet bai lam bang

- Sa bai vao v


- Goi HS nhac lai cac kien thc a hoc trong 2, 3.

- Chot lai cach chng minh hnh thang can - HS neu nh ngha hnh thang, hnh thang can. Tnh chat va dau hieu nhan biet hnh thang can


BTVN.- Bai tap 16 trang 75 Sgk

- Bai tap 19 trang 75 Sgk- On kien thc ve hnh thang, hnh thang can- Bai tap 18 trang 75 Sgk

- Bai tap 19 trang 75 Sgk- HS nghe dan


To duyetBGH duyet

TUAN III

Tiet 5. 4. ng trung bnh cua tam giac* * * * * *I/ MUC TIEU:

- Hoc sinh nam vng nh ngha va cac nh l ve ng trung bnh cua tam giac.

- HS biet ve ng trung bnh cua tam giac, van dung cac nh l e tnh o dai cac oan thang; chng minh hai oan thang bang nhau, hai oan thang song song.

- HS thay c ng dung thc te cua ng trung bnh trong tam giac.

II/ CHUAN B :- GV : Cac bang phu (ghi e kiem tra, ve san hnh 33), thc thang, eke, thc o goc.

- HS: On kien thc ve hnh thang, hnh thang can, giay lam bai kiem tra; thc o goc. III/ PHNG PHP : - Van ap, neu van eIV/ HOAT ONG DAY- HOC :



GV a ra e kiem tra tren bang phu :

Cac cau sau ay cau nao ung? Cau nao sai? Hay giai thch ro hoac chng minh cho ieu ket luan cua mnh.

1. Hnh thang co hai goc ke mot ay bang nhau la hnh thang can.

2. T giac co hai ng cheo bang nhau la hnh thang can.

3. T giac co hai goc ke mot canh bu nhau va co hai ng cheo bang nhau la hnh thang can.

4. T giac co hai goc ke mot canh bang nhau la hnh thang can.

5. T giac co hai goc ke mot canh bu nhau va co hai goc oi bu nhau la hnh thang can.

GV. anh gia, cho iem.- HS len bang tra li (co the ve hnh e giai thch hoac chng minh cho ket luan cua mnh)

- HS con lai chep va lam vao v bai tap :

1- ung (theo nh ngha)

2- Sai (ve hnh minh hoa)

3- ung (giai thch)

4- Sai (giai thch + ve hnh )

5- ung (giai thch)


4. NG TRUNG BNH CUA TAM GIAC- GV gii thieu bai trc tiep ghi bang - HS ghi bai

Hoat ong 3 : Phat hien tnh chat (10)

1. ng trung bnh cua tam giac

a. nh l 1: (sgk)

GT (ABC AD = DB, DE//BC

KL AE =EC

Chng minh (xem sgk) - Cho HS thc hien ?1

- Quan sat va neu d oan ?

- Noi va ghi bang nh l.

- C/minh nh l nh the nao?

- Ve EF//AB.

- Hnh thang BDEF co BD//EF =>?

- Ma AD=BD nen ?

- Xet (ADE va (AFC ta co ieu g ?

- (ADE va (AFC nh the nao?

- T o suy ra ieu g ?

- HS thc hien ?1 (ca the):

- Neu nhan xet ve v tr iem E

- HS ghi bai va lap lai

- HS suy ngh

- EF=BD

- EF=AD

-; AD=EF

- (ADE = (AFC (g-c-g)

- AE = EC

* nh ngha: (Sgk)

DE la ng trung bnh cua (ABC -V tr iem D va E tren hnh ve? - Ta noi rang oan thang DE la ng trung bnh cua tam giac ABC. Vay em nao co the nh ngha ng trung bnh cua tam giac ?

- Trong mot ( co may tr bnh? - HS neu nhan xet: D va E la trung iem cua AB va AC

- HS phat bieu nh ngha ng trung bnh cua tam giac

- HS khac nhac lai. Ghi bai vao v

- Co 3 tr bnh trong mot (

Hoat ong 4 : Tm tnh chat ng trung bnh tam giac (15)

b. nh l 2 : (sgk)

A

D E F

B C

Gt (ABC ;AD=DB;AE = EC

Kl DE//BC; DE = BC

Chng minh : (xem sgk)- Yeu cau HS thc hien ?2

- Goi vai HS cho biet ket qua

- T ket qua tren ta co the ket luan g ve ng trung bnh cua tam giac?

- Cho HS ve hnh, ghi GT-KL

- Muon chng minh DE//BC ta phai lam g?

- Hay th ve them ng ke phu e chng minh nh l

- GV chot lai bang viec a ra bang phu bai chng minh cho HS - Thc hien ?2 ca nhan tai cho.- Neu ket qua kiem tra:

, DE = BC

- HS phat bieu: ng trung bnh cua tam giac

- Ve hnh, ghi GT-KL

- HS suy ngh

- HS ke them ng phu nh gi y thao luan theo nhom nho 2 ngi cung ban roi tra li (neu hng chng minh tai cho)


?3

DE= 50 cm

T DE = BC (nh ly 2)

=> BC = 2DE=2.50=100

Bai 20 trang 79 Sgk

- Cho HS tnh o dai BC tren hnh 33 vi yeu cau:

- e tnh c khoang cach gia hai iem B va C ngi ta phai lam nh the nao?

- GV chot lai cach lam (nh cot noi dung) cho HS nam

- Yeu cau HS chia nhom hoat ong

- Thi gian lam bai 3

- GV quan sat nhac nh HS khong tap trung

- GV nhan xet hoan chnh bai- HS thc hien ? 3 theo yeu cau cua GV:

- Quan sat hnh ve, ap dung kien thc va hoc, phat bieu cach thc hien

- DE la ng trung bnh cua (ABC

=> BC = 2DE

- HS chia lam 4 nhom lam bai

- Sau o ai dien nhom trnh bay

- Ta co =500

=>IK//BC

ma KA=KC (gt)

=>IK la ng trung bnh

nen IA=IB=10cm


BTVN.


- Bai tap 28 trang 80 Sgk- Thuoc nh ngha, nh l 1, 2. Xem lai cach cm nh l 1,2 Sgk


! Tng t bai 20

- Bai tap 28 trang 80 Sgk- HS nghe dan va ghi chu vao v

Tiet 6.4. ng trung bnh cua hnh thang******I/ MUC TIEU:

- Kien thc : HS nam vng nh ngha ve ng trung bnh cuahnh thang; nam vng noi dung nh l 3, nh l 4 ve ng trung bnh hnh thang.

- Ky nang : Biet van dung nh l tnh o dai cac oan thang, chng minh cac he thc ve oan thang.

- Thay c s tng t gia nh ngha va nh l ve ng trung bnh trong tam giac va trong hnh thang; s dung tnh chat ng trung bnh cua tam giac e chng minh cac tnh chat cua ng trung bnh trong hnh thang.

II/ CHUAN B :- GV : Bang phu , thc thang, thc o goc.- HS : On bai ng trung bnh cua tam giac, lam cac bai tap ve nha.

III/ PHNG PHAP : - Qui nap, neu van e , hp tac nhom




1/ nh ngha ng trung bnh cua tam giac.(3)

2/ Phat bieu nh l 1, l 2 ve ng trbnh cua (. (4)

3/ Cho (ABC co E, F la trung iem cua AB, AC. Tnh EF biet BC = 15cm. (3)

- Treo bang phu a ra e kiem tra. Cho HS oc e

- Goi mot HS

- Kiem tra v bai lam vai HS

- Theo doi HS lam bai

- Cho HS nhan xet, anh gia cau tra li va bai lam cua ban

- Cho HS nhac lai ngha, l 1, 2 ve tb cua tam giac

- GV anh gia cho iem.- HS oc e kiem tra , thang iem tren bang phu.

- HS c goi len bang tra li cau hoi va giai bai toan.

- HS con lai nghe va lam bai tai cho

- Nhan xet tra li cua ban, bai lam bang

- HS nhac lai

- T sa sai (neu co)


4. NG TRUNG BNH CUA HNH THANG- GV gii thieu trc tiep va ghi bang: chung ta a hoc ve tb cua tam giac va t/c cua no. Trong tiet hoc nay, ta tiep tuc nghien cu ve tb cua hthang. - HS nghe gii thieu, ghi ta bai vao v

Hoat ong 3 : Tm kien thc mi (11)

2. ng trung bnh cua hnh thanga/ nh l 3: (sgk trg 78)

GT hnh thang ABCD (AB//CD)

AE = ED ; EF//AB//CD

KL BF = FC + Neu ?4 va yeu cau HS thc hien

- Hay neu nhan xet theo yeu cau ?4.- GV chot lai va neu nh l 3

- HS nhac lai va tom tat GT-KL

- Gi y chng minh : I co la trung iem cua AC khong? V sao? Tng t vi iem F?

+ HS thc hien ?4 theo yeu cau cua GV

- Neu nhan xet: I la trung iem cua AC ; F la trung iem cua BC

- oc lai nh l, ve hnh va ghi GT-KL

- Chng minh BF = FC bang cach ve AC cat EF tai I roi ap dung nh l 1 ve tb cua ( trong (ADC va (ABC


nh nghia: (Sgk trang 78)

EF la tb cua hthang ABCD - Cho HS xem tranh ve hnh 38 (sgk) va neu nhan xet v tr cua 2 iem E va F

- EF la ng trung bnh cua hthang ABCD vay hay phat bieu ngha tb cua hnh thang?- Xem hnh 38 va nhan xet: E va F la trung iem cua AD va BC

- HS phat bieu nh ngha

- HS khac nhan xet, phat bieu lai (vai lan)

Hoat ong 5 : Tnh chat ng trung bnh hnh thang (15)

b/nh l 4 : (Sgk)

GT hthang ABCD (AB//CD)

AE = EB ; BF = FC

KL EF //AB ; EF //CD

EF =

Chng minh (sgk)- Yeu cau HS nhac lai nh l 2 ve ng trung bnh cua tam giac

- D oan tnh chat tb cua hthang? Hay th bang o ac?

- Co the ket luan c g?

- Cho vai HS phat bieu nhac lai

- Cho HS ve hnh va ghi GT-KL Gi y cm: e cm EF//CD, ta tao ra 1 tam giac co EF la trung iem cua 2 canh va DC nam tren canh kia o la (ADK

- GV chot lai va trnh bay chng minh nh sgk

- Cho HS tm x trong hnh 44 sgk- HS phat bieu l

- Neu d oan tien hanh ve, o ac th nghiem

- Rut ra ket luan, phat bieu thanh nh l

- HS ve hnh va ghi GT-KL

- HS trao oi theo nhom nho sau o ng tai cho trnh bay phng an cua mnh .

- HS nghe hieu va ghi cach chng minh vao v

- HS tm x trong hnh va tra li ket qua.(x=40m)


Bai 23 trang 80 Sgk

Bai 24 trang 80 Sgk

Bai 25 trang 80 SgkVe nha lam cac bai tap.

- Bai 23 trang 80 Sgk! S dung nh nghia

- Bai 24 trang 80 Sgk! S dung nh l 4

- Bai 25 trang 80 Sgk! Chng minh EK la ng trung bnh cua tam giac ADC

! Chng minh KF la ng trung bnh cua tam giac BCD- HS nghe hng dan va ghi chu vao tap

To duyet

BGH duyet

TUAN IV

Tiet 7.Luyen tap 4* * * * * * I/ MUC TIEU:

- Qua luyen tap, giup HS van dung thanh thao nh l ng trung bnh cua hnh thang e giai c nhng bai tap t n gian en hi kho.

- Ren luyen cho HS cac thao tac t duy phan tch, tong hp qua viec tap luyen phan tch chng minh cac bai toan. II/ CHUAN B : - GV : Bang phu, compa, thc thang co chia khoang.

- HS : On bai (4) , lam bai nha

III/ PHNG PHAP : am thoai, gi m

IV/ HOAT ONG DAY- HOC :NOI DUNG HOAT ONG CUA GV HOAT ONG CUA HS


1- Phat bieu /ngha ve tb cua tam giac, cua hthang. (3)

2- Phat bieu l ve tnh chat cua tb tam giac, tb hthang. (4)

3- Tnh x tren hnh ve sau:(3)

M I

N

P 5dm K x Q- Treo bang phu a ra e kiem tra. Goi mot HS len bang

- Kiem bai tap ve nha cua HS

- Goi HS nhan xet cau tra li va bai lam bang.

- GV chot lai ve s giong nhau, khac nhau gia nh ngha tb tam giac va hnh thang; gia tnh chat hai hnh nay

- HS c goi len bang tra li cau hoi va lam bai

- HS con lai lam vao giay bai 3

- Nhan xet, gop y bang

- HS nghe e hieu sau sac hn ve ly thuyet



GT ABCD la hthang (AB//CD)

AE=ED,FB=FC,KB=KD

KL E,K,F thang hang

Giai

EK la ong trung bnh cua (ABD nen EK //AB (1)

Tng t KF // CD (2)

Ma AB // CD (3)

T (1)(2)(3)=>EK//CD,KF//CD

Do o E,K,F thang hang


Ta co: CD la ng trung bnh cua hnh thang ABFE.

Do o: CE = (AB+EF):2

hay x = (8+16):2 = 12cm

- EF la ng trung bnh cua hnh thang CDHG. Do o :

EF = (CD+GH):2

Hay 16 = (12+y):2

=> y = 2.16 12 = 20 (cm)


GT hnh thang ABCD (AB//CD)

AE = ED ; BF = FC

AF cat BD I, cat AC K

AB = 6cm; CD = 10cm

KL AK = KC ; BI = ID

Tnh EI, KF, IK - Goi HS oc e

- Cho mot HS trnh bay giai

- Cho HS nhan xet cach lam cua ban, sa cho sai neu co

- GV noi nhanh lai cach lam nh li giai

- GV ve hnh 45 va ghi bai tap 26 len bang .

- Goi HS neu cach lam

- Cho ca lp lam tai cho, mot em lam bang

- Cho ca lp nhan xet bai giai bang

- GV nhan xet, sa sai (neu co), cham cho iem

- Neu bai tap 28

- Ve hnh, tom tat GT KL?

- Lu y HS cac k hieu tren hnh ve.

Gi y cho HS phan tch:

a) EF la tb cua hthang ABCD

EF//DC EF//AB

AE=ED EK//DC EI//AB AE=ED

AK = KC BI = ID

-> Goi mot HS trnh bay bai giai bang, mot HS trnh bay mieng

b) Biet AB = 6cm, CD = 10cm co the tnh c EF? KF? EI?

- GV kiem v bai lam mot vai HS va nhan xet

- Hay so sanh o dai IK vi hieu 2 ay hnh thang ABCD?- HS oc lai e bai 25 sgk

- Mot HS len bang trnh bay

- Ca lp theo doi, nhan xet, gop y sa sai

- T sa sai vao v

GT ABCD la hthang (AB//CD)

AE=ED,FB=FC,KB=KD

KL E,K,F thang hang

EK la ong trung bnh cua (ABD nen EK //AB (1)

Tng t KF // CD (2)

Ma AB // CD (3)

T (1)(2)(3)=>EK//CD,KF//CD

Do o E,K,F thang hang

- HS oc e,ve hnh vao v.

- HS len bang ghi GT- KL

GT AB//CD//EF//GH

AC= CE=EG; BD=DF=FH

KL Tnh x, y

- HS suy ngh, neu cach lam

- Mot HS lam bang, con lai lam ca nhan tai cho

- HS lp nhan xet, gop y bai giai bang

- CD la ng trung bnh cua hnh thang ABFE.

Do o: CE = (AB+EF):2

hay x = (8+16):2 = 12cm

- EF la ng trung bnh cua hnh thang CDHG. Do o :

EF = (CD+GH):2

Hay 16 = (12+y):2

=> y = 2.16 12 = 20 (cm)

- HS oc e bai (2 lan)

- Mot HS ve hnh, tom tat GT-KL len bang, ca lp thc hien vao v

Tham gia phan tch, tm cach chng minh.

- Mot HS giai bang, ca lp lam vao v

a) EF la tb cua hthang ABCD

nen EF//AB//CD.

K( EF nen EK//CD va AE = ED ( AK = KC (l tb (ADC)

I( EF nen EI//AB va AE=ED (gt)

( BI = ID (l tb (DAB)

b) EF=(AB+CD)=(6+10)=8cm

EI = AB = 3cm

KF = AB = 3cm

IK=EF(EI+KF)=8(3+3)=2cm

- HS suy ngh, tra li:

IK = (CD AB)


Bai 27 trang 80 Sgk

BTVN.

- Bai 27 trang 80 Sgk

a) S dung tnh chat ng trung bnh cua tam giac ABC

b) s dung bat ang thc tam giac (EFK)

- On tap cac bai toan dng hnh a hoc lp 6, lp 7 - HS nghe dan

- Ghi nhan vao v

Tiet 85 Dng hnh bang thc va compa. Dng hnh thang* * * * * *I/ MUC TIEU:

- HS hieu c khai niem Bai toan dng hnh. o la bai toan ve hnh ch s dung hai dung cu la thc va compa; Bc au, HS hieu c rang giai mot bai toan dng hnh la ch ra mot he thong cac phep dng hnh c ban lien tiep nhau e xac mh c hnh o (cach dng) va phai ch ra c rang hnh dng c theo phng phap a neu ra thoa man ay u cac yeu cau at ra (chng minh).

- HS bc au biet trnh bay phan cach dng va chng minh; biet s dung thc va compa e dng hnh vao trong v (theo cac so lieu cho trc bang so) tng oi chnh xac.

- Ren luyen tnh can than, chnh xac khi s dung dung cu; ren luyen kha nang suy luan khi chng minh. Co y thc van dung dng hnh vao thc te.

II/ CHUAN B : :

- GV : thc thang, compa, thc o goc, cac bang phu e ve hnh san.

- HS : On tap cac bai toan dng hnh a hoc lp 6, 7; v ghi, sgk, dung cu hoc tap III/ PHNG PHAP : am thoai, gi m.IV/ HOAT ONG DAY- HOC :


Hoat ong 1 : Vao bai mi (1)

5 DNG HNH BANG THC VA COMPA

DNG HNH THANG

- lp 6,7 cac em a lam quen vi cac dung cu ve hnh. Hom nay chung ta se ve hnh ch vi 2 dung cu : thc, compa- HS nghe va ghi ta bai

Hoat ong 2 : Tm hieu khai niem bai toan dng hnh (4)

1.Bai toan dng hnh:

- Bai toan ve hnh ma ch s dung hai dung cu la thc va compa c goi la bai toan dng hnh . - GV thuyet trnh cho HS nam va phan biet ro cac khai niem bai toan dng hnh, ve hnh, dng hnh

- Khi dung thc ta ve c hnh nao ?

- Vi compa th sao ?

- HS nghe giang.

- Ve 1 g thang khi biet 2 iem

- Ve 1 n thang khi biet 2 mut

- Ve 1 tia khi biet goc va 1 iem cua tia.

-Ta ve c tron khi biet tam

Hoat ong 3 : On tap kien thc cu (12)

2.Cac bai toan dng hnh a biet:

- Dng oan thang bang oan thang cho trc.

- Dng goc bang goc cho trc

- Dng ng trung trc cua mot oan thang cho trc, dng trung iem cua mot oan thang cho trc.

- Dng tia phan giac cua mot goc cho trc.

- Dng ng thang i qua mot iem cho trc va vuong goc vi ng thang cho trc

- Dng ng thang i qua mot iem cho trc va song song vi ng thang cho trc.

- Dng tam giac biet ba canh (hoac hai canh va goc xen gia hoac biet mot canh va hai goc ke)- GV a ra bang phu co ve hnh bieu th li giai cac bai toan dng hnh a biet (H46, 47 Sgk).

- Cac hnh ve trong bang, moi hnh bieu th noi dung va li giai cua bai toan dng hnh nao?

- Mo ta th t cac thao tac s dung compa va thc thang e ve c hnh theo yeu cau cua moi bai toan

- GV chot lai bang cach trnh bay cac thao tac s dung compa, thc thang trong tng bai toan tren va cho biet: 6 bai toan tren va 3 bai dng tam giac la 9 bai c coi nh a biet, ta se s dung e giai cac bai toan dng hnh khac. Khi trnh bay li giai bai toan dng hnh, th khong phai trnh bay thao tac ve nh a lam ma ch ghi vao phan li giai nh la mot thong bao ch dan co phep dng hnh o trong cac bc dng hnh ma thoi - HS quan sat hnh ve va suy ngh tra li

Hnh 46:

a) Dng oan thang

b) Dng goc

c) Dng trung trc . . .

Hnh 47:

a) Dng tia phan giac

b) Dng ng vuong goc

c) Dng t song song

- HS quan sat va thc hanh dng hnh vao v cac bai tren

- HS nghe e biet s dung cac bai toan dng hnh c ban vao viec giai bai toan dng hnh

Hoat ong 3 : Tm hieu dng hnh thang (18)

3.Dng hnh thang:

V du: Dng hnh thang ABCD biet ay AB = 3cm, CD = 4cm, canh ben AD = 2 . D = 700

Cach dng:

- Dng (ACD co D = 700, DC = 4cm, DA = 2cm

- Dng tia Ax song song vi CD

- Dng iem B tren tia Ax sao cho AB=3cm. Ke oan thang CB

Chng minh:

- Theo cach dng, ta co AB//CD nen ABCD la hnh thang

- Theo cach dng (ACD, ta co D = 700, DC = 4cm, DA = 2cm.

- Theo cach dng iem B, ta co AB = 3cm.

Vay ABCD la hnh thang thoa man cac yeu cau cua e bai - Ghi v du trong sgk cho HS tm hieu Gt va Kl cua bai toan

- Em hay cho biet GT-KL cua bai toan nay?

- Treo bang phu co ve trc hnh thang ABCD can dng: Gia s a dng c hnh thang ABCD thoa man cac yeu cau e bai.

- Muon dng hnh thang ta phai xac nh 4 nh cua no. Theo cac em, nhng nh nao co the xac nh c? V sao?

- T phan tch, ta suy ra cach dng

- Ta phai chng minh t giac ABCD la hnh thang thoa man cac yeu cau e ra. Em nao co the chng minh c?

- GV chot lai va ghi bang phan chng minh

- Vi cach dng tren, ta co the dng c bao nhieu hnh thoa man y/c e bai? V sao?

- GV neu phan bien luan bai - HS oc va tm hieu e bai

- HS phat bieu tom tat GT-KL cua bai toan

- HS quan sat

- (ACD xac nh c v biet hai canh va goc xen gia (xac nh c 3 nh A, C, D)

iem B nam tren ng thang ssong vi CD, cach A mot khoang 3cm

- HS tham gia neu cach dng

- HS lan lt neu cac bc cm t giac ABCD la hnh thang thoa man cac yeu cau e ra

- HS ghi bai

- HS suy ngh, tra li

- HS nghe hieu

Hoat ong 4: Cung co (8)

Bai 29 trang 83 Sgk

1. Giai bai toan dng hnh gom 4 phan: Phan tch Cach dng Chng minh Bien luan.

2. Li giai mot bai dng hnh ch yeu cau hai phan: cach dng va chng minh. - Bai 29 trang 83 Sgk+ Cho HS neu cach dng

- Goi 1 HS chng minh

- GV chot lai cach giai mot bai toan dng hnh (4 bc); cach tien hanh tng bc

- GV nhan manh cach trnh bay li giai bai toan dng hnh va lu y can phai phan tch ngoai nhap- HS oc e va neu cach dng- Dng oan thang BC=4cm

- Dng tia Bx tao vi tia BC 1 goc CBx = 650- Dng ng thang qua C va vuong goc vi Bx ng thang nay cat tia Bx tai A

- (ABC co=900 (v CABx)

BC=4cm,

- HS nghe, hieu

- HS nhac lai 4 bc tien hanh giai mot bai toan dng hnh

- HS nhac lai cach trnh bay li giai mot bai toan dng hnh

Hoat ong 5: Dan do (2)

BTVN.

Bai 30 trang 83 Sgk

Bai 31 trang 83 Sgk- Bai 30 trang 83 Sgk

! Tng t bai 29

- Bai 31 trang 83 Sgk! Ve (ADC co

AD=2cm, AC=4cm,DC=4cm

Chu y can phan tch bai toan e ch ra cach dng. - Trong li giai ch ghi hai phan cach dng va chng minh - HS nghe dan

- Ghi chu vao v bai tap

To duyet

BGH duyet

TUAN V

Tiet 9. Luyen tap 5* * * * * *I/ MUC TIEU :- HS c ren luyen ky nang trnh bay phan cach dng va chng minh trong li giai bai toan dng hnh; c tap phan tch bai toan dng hnh ch e ch ra cach dng.

- HS s dung compa thc thang e dng c hnh vao trong v.

II/ CHUAN B : :

- GV : Compa, thc thang, thc o goc.

- HS : Hoc va lam bai nha, v ghi, sgk, dung cu HSIII/ PHNG PHAP: Van ap, hp tac nhom




1/ Cac bc giai bai toan dng hnh? (3)

2/ Dng (ABC vuong tai B , biet canh huyen AC = 4 cm , canh goc vuong BC = 2cm(7) - Treo bang phu. Goi mot HS len bang

- Kiem bai tap ve nha cua HS

- Cho HS nhan xet bang - Mot HS len bang,ca lp theo doi CD + Dng oan BC = 2cm

+ Dng Bx ( BC tai B

+ Dng cung tron tam la iem C vi ban knh 4cm, cung nay cat tia Bx iem A. Noi AC

(ABC la tam giac can dng

+ Chng minh :

Do Bx(BC=>=900=>(ABC vuong tai B co BC=2cm AC=4cm

- HS khac nhan xet


Bai 33 trang 83 Sgk

Cach dng:

+ Dng oan CD = 3cm

+ Qua D dng Dx tao vi Dy 1 goc 800

+ Dng cung tron tam C ban knh 4cm.Cung nay cat Dx tai A

+ Qua A dng tia Az // DC

+ Dng cung tron tam D ban knh 4cm .Cung nay cat Az tai B

Chng minh:

ABCD la hnh thang v AB//CD

Hnh thang ABCD la hnh thang can v co hai ng cheo AC = BD = 4cm.

Hnh thang can ABCD co = 800, CD = 3cm, AC = 4cm thoa man yeu cau e bai.

Bai 34 trang 83 Sgk

- Cach dng :

+ Dng oan CD = 3cm

+ Qua D dng tia Dx tao vi CD mot goc 900

+ Dng cung tron tam D ban knh 2cm. Cung nay cat Dx tai iem A

+ Qua A dng tia Ay // DC

+ Dng cung tron tam C ban knh 3cm . Cung nay cat tia Ay tai B

Chng minh

+ Do AB//CD=>ABCD la hnh thang co co = 900, CD = 3cm, AD = 2cm thoa man yeu cau e bai.Bai 33 trang 83 Sgk

- Yeu cau HS hp tac theo nhom nho cung ban vi yeu cau :

- Ve hnh gia s dng c thoa man cac yeu cau cua bai toan.

- Thi gian thao luan la 5

- Ch ra cach dng tng bc.

+ Trc tien ta dng oan nao ?

+ Muon dng goc D bang 800 ta lam sao ?

+ Muon dng canh AC = 4cm ta lam nh the nao ?

+ Muon co hnh thang ta phai co ?

+ Xac nh iem B nh the nao ?

- Trnh bay hoan chnh bai giai

- Hng dan cach chng minh

+ AB // CD ta co ieu g ?

+ Co AC = BD = 4cm ta suy ra ieu g ?

+ Ket luan ?

Bai 34 trang 83 Sgk

- Chia nhom hoat ong. Thi gian lam bai la 5 cho cach dng va 2 cho chng minh

- Nhac nh HS khong tap trung lam bai.

- Yeu cau ai dien nhom trnh bay. Cac nhom nhan xet

- GV hoan chnh bai

- Lu y HS co hai hnh thang can dng do cung tron tam C cat Ay tai 2 iem- HS oc e bai

- Lam bai theo nhom ngoi cung ban : thao luan cach dng va chng minh.

- ai dien nhom ghi len bang

+ Dng oan CD = 3cm

+ Qua D dng tia Dx tao vi tia Dy 1 goc 800

+ Dng cung tron tam C ban knh 4cm. Cung nay cat Dy tai iem A

+ Qua A dng tia Az // DC

+ Dng cung tron tam D ban knh 4cm . Cung nay cat tia Az tai B

- Ca lp nhan xet

- HS tra li theo cau hoi gi y

+ Co ABCD la hnh thang

+ Hnh thang ABCD co 2 ng cheo bang nhau la hnh thang can

+ Hnh thang can ABCD co

AC = 4cm, CD= 3cm,=800 thoa man yeu cau e bai

HS ghi bai giai hoan chnh tap

- HS oc e bai

- HS chia lam 4 nhom hoat ong

- Cach dng

+ Dng oan CD = 3cm

+ Qua D dng tia Dx tao vi CD mot goc 900

+ Dng cung tron tam D ban knh 2cm. Cung nay cat Dx tai iem A

+ Qua A dng tia Ay // DC

+ Dng cung tron tam C ban knh 3cm . Cung nay cat tia Ay tai B

Chng minh

+ Do AB // CD => ABCD la hnh thang co co = 900, CD = 3cm, AD = 2cm thoa man yeu cau e bai.


- Cac nhom nhan xet lan nhau

- HS ghi vao tap


BTVN.

Bai 32 trang 83 Sgk


! Dng tam giac eu sau o dng tia phan giac cua 1 goc

- Xem lai kien thc ve ng trung bnh va xem trc noi dung bai mi 6.- HS ghi chu vao tap

Tiet 10: 6. oi xng trucI/ MUC TIEU :- HS nam vng nh ngha hai iem oi xng vi nhau qua mot ng thang; hieu c nh ngha ve hai hnh oi xng vi nhau qua mot ng thang; nhan biet c hai oan thang oi xng vi nhau qua mot ng thang; hieu c nh ngha ve hnh co truc oi xng va qua o nhan biet c mot hnh thang can la hnh co truc oi xng.

- HS biet ve iem oi xng vi mot iem cho trc, ve oan thang oi xng vi oan thang cho trc qua mot ng thang. Biet c/m hai iem oi xng vi nhau qua mot mot ng thang.

- HS biet nhan ra mot so hnh co truc oi xng trong thc te. Bc au biet ap dung tnh oi xng truc vao viec ve hnh, gap hnh.

II/ CHUAN B :

- GV : Giay ke o vuong, bang phu, thc

- HS : On ng trung trc cua oan thang; hoc va lam bai nha

- Phng phap : Van ap, trc quan

III/ HOAT ONG DAY- HOC :



- Hay dng mot goc bang 300

A

B C

D

E

- Treo bang phu. Goi mot HS lam bang va yeu cau cac HS khac lam vao tap

- Kiem tra bai tap ve nha cua HS


- Hoan chnh bai lam, cho iem- Mot HS len bang trnh bay:

-Cach dng:

+ Dng tam giac eu ABC

+ Dng phan giac cua mot goc chang han goc A ta c goc =300

Chng minh:

- Theo cach dng (ABC la tam giac eu nen = 600

- Theo cach dng tia phan giac AE ta co = =

= 600 = 300

- HS nhan xet


6. OI XNG TRUC- Qua bai toan tren, ta thay:

B va C la hai iem oi xng vi nhau qua ng thang AE; Hai oan thang AB va AC la hai hnh oi xng nhau qua ng thang AE. Tam giac ABC la hnh co truc oi xng

- e hieu ro cac khai niem tren, ta nghien cu bai hoc hom nay. - HS nghe gii thieu, e y cac khai niem mi

- HS ghi ta bai vao tap

Hoat ong 3 : Hai iem oi xng nhau qua mot ng thang (12)

1. Hai iem oi xng nhau qua mot ng thang :

\

a) nh ngha : (Sgk)

b) Qui c : (Sgk) - Neu ?1 (bang phu co bai toan kem hnh ve 50 sgk)

- Yeu cau HS thc hanh

- Noi: A la iem oi xng vi iem A qua ng thang d, A la iem x vi A qua d => Hai iem A va A la hai iem oi xng vi nhau qua ng thang d. Vay the nao la hai iem x nhau qua d?

- GV neu qui c nh sgk - HS thc hanh ?1 :

- Mot HS len bang ve, con lai ve vao giay.

- HS nghe, hieu

- HS phat bieu nh ngha hai iem oi xng vi nau qua ng thang d

Hoat ong 4 : Hai hnh oi xng qua mot ng thang (10)

2. Hai hnh oi xng qua mot ng thang:

nh ngha: (sgk)

C B

A

d

A C

B

Hai oan thang AB va AB oi xng nhau qua ng thang d.

d goi la truc oi xng

Lu y: Neu hai oan thang (goc, tam giac) oi xng vi nhau qua mot ng thang th chung bang nhau. - Hai hnh H va H khi nao th c goi la hai hnh oi xng nhau qua ng thang d?

- Neu bai toan ?2 kem hnh ve 51 cho HS thc hanh

B

A

d

- Noi: iem oi xng vi moi iem C( AB eu ( ABva ngc lai Ta noi AB va AB la hai oan thang oi xng nhau qua d. Tong quat, the nao la hai hnh oi xng nhau qua mot ng thang d?

- Gii thieu truc oi xng cua hai hnh

- Treo bang phu (hnh 53, 54):

- Hay ch ro tren hnh 53 cac cap oan thang, ng thang xng nhau qua d? giai thch?

- GV ch dan tren hnh ve chot lai

- Neu lu y nh sgk - HS nghe e phan oan

- Thc hanh ?2 :

- HS len bang ve cac iem A, B, C va kiem nghiem tren bang

- Ca lp lam tai cho

- iem C thuoc oan AB

HS neu nh ngha hai hnh oi xng vi nhau qua ng thang d

- HS ghi bai

- HS quan sat, suy ng va tra li:

+ Cac cap oan thang x: AB va AB, AC va AC, BC va BC

+ Goc: ABC va ABC,

+ ng thang AC va AC

+ (ABC va (ABC

Hoat ong 5 : Hnh co truc oi xng (8)

3. Hnh co truc oi xng:

a) nh nghia : (Sgk)

A

ng thang AH

la truc oi xng

cua (ABC

B H C

b) nh l : (Sgk)

A H B

D K C

ng thang HK la truc oi xng cua hnh thang can ABCD- Treo bang phu ghi san bai toan va hnh ve cua ?3 cho HS thc hien.

- Hoi:

+ Hnh x vi canh AB la hnh nao? oi xng vi canh AC la hnh nao? oi xng vi canh BC la hnh nao?

- GV noi cach tm hnh oi xng cua cac canh va chot lai van e, neu nh ngha hnh co truc oi xng

- Neu ?4 bang bang phu

- GV chot lai: mot hnh H co the co truc oi xng, co the khong co truc oi xng

- Hnh thang can co truc oi xng khong ? o la ng thang nao?

- GV chot lai va phat bieu nh l - Thc hien ?3 :

- Ghi e bai va ve hnh vao v

- HS tra li : oi xng vi AB la AC; oi xng vi AC la AB, oi xng vi BC la chnh no

- Nghe, hieu va ghi chep bai

- Phat bieu lai nh ngha hnh co truc oi xng.

- HS quan sat hnh ve va tra li

- HS nghe, hieu va ghi ket luan cua GV

- HS quan sat hnh, suy ngh va tra li

- HS nhac lai nh l


Bai 35 trang 87 Sgk

Bai 37 trang 87 Sgk- Bai 35 trang 87 Sgk

! Treo bang phu va goi HS len ve


! Cho HS xem hnh 59 sgk va hoi : Tm cac hnh co truc oi xng - HS len ve vao bang

- HS quan sat hnh va tra li :

+ Hnh a co 2 truc oi xng

+ Hnh b co 1 truc oi xng

+ Hnh c co 1 truc oi xng

+ Hnh d co 1 truc oi xng

+ Hnh e co1 truc oi xng

+ Hnh g khong co truc oi xng

+ Hnh h co 5 truc oi xng

+ Hnh i co 2 truc oi xng


BTVN.

Bai 36 trang 87 Sgk

Bai 38 trang 87 SgkBai 36 trang 87 Sgk

! Hai oan thang oi xng th bang

Bai 38 trang 87 Sgk! Xep 2 hnh gap lai vi nhau

- Hoc bai : thuoc cac nh ngha - HS s dung tnh chat bac cau

- HS lam theo hng dan

To duyet

BGH duyet

TUAN VI

Tiet11. Luyen tap 6.* * * * * *I/ MUC TIEU : - Nhan biet hnh co truc oi xng trong thc te . Van dung tnh oi xng truc e ve, gap hnh

II/ CHUAN B : :

- GV : Compa, thc thang, thc o goc.

- HS : Hoc va lam bai nha, v ghi, Sgk, dung cu HS

III/PHNG PHAP : Van ap, gi m




1/ Hai iem goi la oi xng nhau qua ng thang d neu .......

2/ Bai 36a trang 87 Sgk

- Treo bang phu. Goi HS len bang lam. Ca lp cung lam


- Goi HS nhan xet

- GV anh gia cho iem- HS len bang ien

1/ Hai iem goi la oi xng nhau qua ng thang d neu d la ng trung trc noi hai iem o

2/ Ta co A oi xng vi B qua OyNen Oy la ng trung trc cua AB

OA=OB (1)

Tng t Ox la ng trung trc cua AC

OA=OC (2)

T (1)(2) suy ra OB=OC

- HS khac nhan xet


Bai 36b trang 87 Sgk

Ta co (AOB la tam giac can v OB=OA

Nen Oy la tia phan giac cua

Suy ra

Tng t :

Vay= 2()

=>

Bai 39 trang 88 Sgk

a)C oi xng vi A qua d, Ddnen AD = CD

AD+DB=CD+DB = CB(1)

Tng t oi vi iem E ta co

AE = EC

=> AE+EB = CE+EB (2)

Trong (BEC th

CB< CE+EB (3)

T (1)(2)(3) ta co

AD+DB < AE+EB

b) V AE+EB > BC suy ra

AE+EB > AD+DB

Nen con ng ngan nhat ma tu phai i la i theo ADB

Bai 40 trang 88 Sgk

a) Co mot truc oi xng

b) Co mot truc oi xng

c) Khong co truc oi xng

d) Co mot truc oi xng

Bai 36b trang 87 Sgk

GV lan lt hoi

- (AOB la tam giac g ? V sao ?

- Ma Ox la ng trung trc cua AB nen ta co ieu g ? Suy ra ?

- Tng t ta co ieu g ?

- Cong ta c g ?

- Ma =?,=?

- Goi HS len bang trnh bay

- Cho HS nhan xet

Bai 39 trang 88 Sgk

- Goi HS ve hnh. Neu GT- KL

a) C oi xng vi A qua d, Dd nen ta co ieu g ?

- AD+DB= ?

- Tng t oi vi iem E ta co ?

- AE+EB=?

- Trong (BEC th CB nh the nao vi CE+EB ?

- T (1)(2)(3) ta co ieu g ?

- Cho HS len bang trnh bay lai

b) V AE+EB > BC suy ra?

- Nen con ng ngan nhat ma tu phai i la ?

- Goi HS nhan xet

- GV hoan chnh

Bai 40 trang 88 Sgk

- Treo bang phu ghi hnh 61

- Cho HS nhan xet

HS tham gia tra li

- (AOB la tam giac can v OB=OA

- Nen Ox la tia phan giac cua

- Suy ra

- Tng t :

-= 2()

-

- HS len bang trnh bay lai

- HS khac nhan xet

- HS len bang ve hnh, neu GT-KL

- AD = CD

- AD+DB = CD+DB = CB (1)

- AE = EC

- AE+EB = CE+EB (2)

- CB < CE+EB (3)

- AD+DB < AE+EB

- HS len bang trnh bay

- AE+EB > AD+DB

- Nen con ng ngan nhat ma tu phai i la i theo ADB

- HS nhan xet

- HS quan sat va tra li

a) Co mot truc oi xng

b) Co mot truc oi xng

c) Khong co truc oi xng

d) Co mot truc oi xng

- HS khac nhan xet


Bai 41 trang 88 Sgk

a) Neu ba iem thang hang th ba iem oi xng vi chung qua mot truc cung thang hang

b) Hai tam giac oi xng vi nhau qua mot truc th co chu vi bang nhau

c) Mot ng tron co vo so truc oi xng

d) Mot oan thang ch co mot truc oi xngBai 41 trang 88 Sgk

- Cho HS oc va tra li

- Cho HS nhan xet

- GV chot lai van e

+ Bat k mot ng knh nao cung eu la truc oi xng cua ng tron

+ Mot oan thang co hai truc oi xng la : ng trung trc cua no va ng thang cha oan thang ay- HS oc e va tra li

a) ung b) ung

c) ung d) Sai

- HS nhan xet

- HS chu y nghe va ghi vao tap


BTVNBai 42 trang 88 Sgk

Bai 42 trang 88 Sgk

! Nhng ch cai ta co the gap lai e cat se co truc oi xng

- Ve nha xem Co the em cha biet va xem trc bai mi 7.- HS ghi chu vao tap

Tiet127. Hnh bnh hanh* * * * * *I/ MUC TIEU :- HS nam vng nh ngha hnh bnh hanh la t giac co cac cap canh oi song song, nam vng cac tnh chat ve canh oi, goc oi va ng cheo cua hnh bnhn hanh; nam vng nam dau hieu nhan biet hnh bnh hanh.

- HS da vao tnh chat va dau hieu nhan biet e ve c dang cua mot hnh bnh hanh, biet chng minh mot t giac la hnh bnh hanh, chng minhn cac oan thang bang nhau, cac goc bang nhau, hai ng thang song song.

II/ CHUAN B :- GV : Thc chia khoang, giay ke o vuong, compa, bang phu (e kiem tra, hnh ve).

- HS : On tap hnh thang, lam bai nha; dung cu: thc thang, compa

III/PHNG PHAP : Qui nap, van apIII/ HOAT ONG DAY- HOC : NOI DUNG HOAT ONG CUA GV HOAT ONG CUA HS


(on lai kien thc cu co lien quan en bai hoc mi)

1 - nh ngha hnh thang, hnh thang vuong, hnh thang can.

2 - Neu cac tnh chat cua hnh thang, cua hnh thang can.

3 - Neu cach chng minh mot t giac la mot hnh thang, hnh thang can. - GV lan lt neu cau hoi (tng khai niem, tnh chat ) va ch nh tng HS tra li. Goi HS khac nhan xet trc khi sang khai niem tiep theo

- GV chot lai bang cach nhac lai nh ngha va tnh chat cua hnh thang, hnh thang can co kem theo hnh ve (bang phu) - HS ng tai cho tra li (theo s ch nh cua GV)

- HS khac nhan xet hoac nhac lai tng khai niem, tnh chat

- HS nghe e nh lai nh ngha, tnh chat cua hnh thang


7. HNH BNH HANH- Treo bang phu ghi hnh 65 trang 90 Sgk va hoi :

! Khi hai a can nang len va ha xuong ABCD luon luon la hnh g - HS nghe e biet c noi dung, ten goi cua bai hoc mi

- HS ghi ta bai


1.nh ngha :

Hnh bnh hanh la t giac co cac canh oi song song

A B

D C

T giac ABCD AB//CD

la hnh bnh hanh ( AD//BC

Hnh bnh hanh la hnh thang co hai canh ben song song. - Cho HS lam ?1 bang cach ve hnh 66 sgk va hoi:

- Cac canh oi cua t giac ABCD co g ac biet?

- Ngi ta goi t giac nay la hnh bnh hanh. Vay theo cac em the nao la mot hnh bnh hanh?

- GV chot lai nh ngha, ve hnh va ghi bang

- nh ngha hnh thang va hnh bnh hanh khac nhau cho nao?

- GV phan tch e HS phan biet va thay c hbh la hthang ac biet - Thc hien ?1 , tra li:

- T giac ABCD co AB//CD va AD//BC

- HS neu ra nh ngha hnh bnh hanh (co the co cac nh ngha khac nhau)

- HS nhac lai va ghi bai

- Hnh thang = t giac + mot cap canh oi song song

- Hnh bnh hanh = t giac + hai cap canh oi song song

Hoat ong 4 : Tnh chat (10)

2. Tnh chat :

nh l :

A B A B

1 1

1 O 1

D C D C

GT ABCD la hnh bnh hanh

AC cat BD tai O

KL a) AB = DC ; AD = BC

b) ;

c) OA = OC ; OB = OD

Chng minh:

(Sgk trang 91)

- Neu ?2 , Bang cach thc hien phep o, hay neu nhan xet ve goc, ve canh, ve ng cheo cua hnh bnh hanh ?

- Gii thieu nh l Sgk (tr 90)

Hay tom tat GT KL va chng minh nh l?

! Gi y: hay ke them ng cheo AC

- Goi HS len bang tien hanh chng minh tng y

- GV theo doi, giup HS yeu

- Goi HS khac nhan xet, bo sung bai chng minh bang

- GV chot lai va neu cach chng minh nh sgk - Tien hanh o va neu nhan xet: AB=DC,AD=BC ;,; AC BD

- HS oc nh l (2HS oc)

- HS tom tat GT-KL va tien hanh chng minh (ca lp cung lam):

a) Hnh bnh hanh ABCD co AD//BC ( AD = BC, AB = CD (tnh chat canh ben hnh thang)

b) (ABC = (CDA (c.c.c)

(

(ADB = (CBD (c.c.c)

(

c) (AOB = (COD (g.c.g)

( OA = OC ; OB = OD

Hoat ong 5 : Dau hieu nhan biet hnh bnh hanh (10)

3. Dau hieu nhan biet hnh bnh hanh:

a) T giac co cac canh oi song song la hnh bnh hanh

b) T giac co cac canh oi bang nhau la hnh bnh hanh

c) T giac co hai canh oi song song va bang nhau la hnh bnh hanh

d) T giac co cac goc oi bang nhau la hnh bnh hanh

e) T giac co hai ng cheo cat nhau tai trung iem cua moi ng la hnh bnh hanh

(Sgk trang 91)

- Hay neu cac menh e ao cua nh l ve tnh chat hbhanh ?

! Lu y HS them t t giac co

- a ra bang phu gii thieu cac dau hieu nhan biet mot t giac la hnh bnh hanh

- Ve hnh len bang, hoi: Neu t giac ABCD co AB // CD,AB = CD Em hay chng minh ABCD la hnh bnh hanh (dau hieu 3)?

- Goi HS khac nhan xet

- GV hoan chnh

- Treo bang phu ghi ?3- HS oc lai nh l va phat bieu cac menh e ao cua nh l

- HS oc (nhieu lan) tng dau hieu

- HS ng tai cho chng minh

Ta co :

AC canh chung

(AD//BC)

AD = BC (gt)

Vay (ABC = (CDA (c.g.c)

=>

Nen : AB//CD

Do o : ABCD la hnh bnh hanh (t giac co cac canh oi ssong)

- HS khac nhan xet

- HS lam ?3

a) ABCD la hnh bnh hanh v co cac canh oi bang nhau

b) EFHG la hnh bnh hanh v co cac goc oi bang nhau

c) INKM khong phai la hnh bnh hanh

d) PSGQ la hnh bnh hanh v co hai ng cheo cat nhau tai trung iem cua moi ng

e) VUYX la hnh bnh hanh v co hai canh oi ssong va bang nhau



- ABCD , EFGH , MNPQ la hnh bnh hanh



ED=EA ; FB=FC

KL BE=DF

Chng minh

Ta co :

DE//BF (v AD//BC (gt)) (1)

DE=1/2AD; BF=1/2BC

ma AD=BC (gt)

Nen DE=BF (2)

T (1)^(2) suy ra ABCD la hnh bnh hanh (dau hieu )Bai tap 43 trang 92 Sgk

- Treo bang phu hnh 71 trang 92 Y/C hs tra li.- Goi HS nhan xet

Bai tap 44 trang 92 Sgk- Goi HS len bang ve hnh, ghi GT KL

- Muon BE=AD ta phai chng minh ieu g ?

- T giac BEDF can yeu to nao la hnh bnh hanh ?

- V sao DE//BF ?

- V sao DE=BF ?


- Cho HS nhan xet

- GV hoan chnh bai

- ABCD , EFGH , MNPQ la hnh bnh hanh

- HS nhan xet

- HS len bang ve hnh,ghi GT-KL

- Ta phai chng minh BEDF la hnh bnh hanh

- DE//BF va DE=BF

- V AD//BC (gt)

- V DE= AD ; BF=BC

ma AD=BC (gt)

-1 HS len bang trnh bay

- HS khac nhan xet

- HS ghi bai


BTVN


Bai tap 45 trang 92 Sgk- Treo bang phu ve hnh bai 45

! Chng minh (cung bang )

- Ve xem lai nh ngha,tnh chat cac dau hieu nhan biet hnh bnh hanh- HS ghi chu vao tap

To duyet

BGH duyet

TUAN VII

Tiet 13. .Luyen tap 7.

* * * * * *I/ MUC TIEU :- Ren ky nang van dung dau hieu nhan biet hnh bnh bnh hanh e chng minh t giac la hnh bnh hanh va suy dien them cach chng minh oan thang, goc bang nhau, 3 iem thang hang, hai ng thang song song.

II/ CHUAN B :- GV : Bang phu, thc ke, phan mau

- HS : On oi xng truc ; hoc va lam bai nha

III. PHNG PHAP : Van ap, hp tac theo nhom




Cho hnh ve

Cho ABCD la hnh bnh hanh. AHBD CKBD

Chng minh: (AHD=(CKB- Treo bang phu . Cho HS oc de

- Goi HS len bang lam

- Ca lp cung lam vao tap


- Cho HS nhan xet

- GV anh gia cho iem - HS oc e

- HS len bang lam bai

Xet (AHD va (CKB co : (AHBD,CKBD)

AD=BC (ABCD la hnh bnh hanh )

( v AD//BC)

Vay (AHD =(CKB ( canh huyen goc nhon )

- HS nhan xet

- HS sa bai vao tap


Bai 47 trang 93 Sgk


AHBD CKBD

OH = OK

KL a) AHCK la hnh bnh

hanh

b) A,O,C thang hang

Chng minh

a) Xet (AHD va (CKB co (v HBD CKBD )

AD=BC (ABCD la hbh )

( v AD//BC )

Vay (AHD =(CKB

( canh huyen goc nhon )

=> AH = CK

Ta co AHBD

CKBD

=>AH//CK(cung//vi BD)

Do o AHCK la hnh bnh hanh ( 2 canh oi song song va bang nhau )

b) Ta co AC va HK goi la ng cheo ( v AHCK la hnh bnh hanh )

ma O la trung iem cua HK

Nen O cung la trung iem cua AC

Do o A,O,C thang hang

Bai 48 trang 93 Sgk

GT T giac ABCD

EB=EA ; FB=FC

GC=GH ; HA=HD

KL EFGH la hnh g ?

Chng minh

- Ta co : EB=EA (gt) HA=HD (gt)

HE la ng trung bnh cua (ABD

Do o HE // BD

Tng t HE la ng trung bnh cua (CBD

Do o EG// BD

Nen HE // GF (cung // vi BD)

Chng minh tng t ta co :

EF // GH

Vay EFGH la hnh bnh hanh

( 2 cap canh oi song song )Bai 47 trang 93 Sgk

- Cho HS oc e va phan tch e bai

- e bai cho ta ieu g ?

- ABCD la hnh bnh hanh noi len ieu g ?

- e bai yeu cau ieu g ?

- Ta co may dau hieu chng minh 1 t giac la hnh bnh hanh ?

- e chng minh AHCK la hnh bnh hanh ta can dau hieu nao ?

- Da vao bai lam khi tra bai ta co ieu g ? T o suy ra ieu g ?

- Vay ta can them ieu kien g th AHCK la hnh bnh hanh ?

- Ta co AHBD ; CKBD =>?- Cho HS len bang trnh bay

- Goi HS nhan xet- e chng minh A,O,C thang hang ta can chng minh ieu g ?

- AHCK la hnh bnh hanh th AC va HK goi la g ?

- Ma O la g cua HK ?

- Do o O la g cua AC ?

- Cho HS len bang trnh bay

- Goi HS nhan xetBai 48 trang 93 Sgk

- Cho HS oc e. Ve hnh neu GT-KL

- Cho HS chia nhom hoat ong . Thi gian lam bai 5

! Noi BD va AC . Da vao dau hieu hai cap canh oi song song . S dung ng trung bnh cua tam giac

- Nhac nh HS cha tap trung

- Goi ai dien nhom len trnh bay

- Cac nhom nhan xet - HS oc e va phan tch

- ABCD la hnh bnh hanh

AHBD CKBD OH = OK

- AB = CD ; AB//CD ; AD = BC ; AD//BC ; ;

- Chng minh AHCK la hnh bnh hanh .

- Chng minh A,O,C thang hang

- HS tra li cac dau hieu

- T giac co 1 cap canh oi va song song va bang nhau

- (AHD =(CKB

=> AH = CK

- AH // CK

- AHBD ; CKBD => AH//CK


- HS nhan xet

- Ta can chng minh O la trung iem AC

- AHCK la hnh bnh hanh th AC va HK goi la ng cheo

- O la trung iem cua HK

- O cung la trung iem cua AC


- HS nhan xet

- HS oc e, ve hnh neu GT-KL

- HS suy ngh ca nhan trc khi chia 4 nhom

- Ta co : EB=EA (gt) HA=HD (gt)

HE la ng trung bnh cua (ABD

Do o HE // BD

Tng t HE la ng trung bnh cua (CBD

Do o EG// BD

Nen HE // GF (cung // vi BD)

Chng minh tng t ta co :

EF // GH

Vay EFGH la hnh bnh hanh ( 2 cap canh oi song song )

- ai dien nhom len trnh bay

- HS nhan xet


1/ Neu ABCD la hnh bnh hanh th :

a) b)

c) d)

2/ T giac co la hnh bnh hanh :

a) va

b) AB=CD va AD=BC

c) va

d) AB=BC va CD=DA

3/ T giac co la hnh bnh hanh :

a) AB=CD va AD//BC

b) AC=BD va AB//CD

c) AD=BC va AB//CD

d) AB=CD va AB//CD- Treo bang phu . Cho HS oc de

- Goi HS len bang ien

- Cho HS nhan xet

- GV hoan chnh- HS oc e

- HS len bang

1c 2b 3d

- HS nhan xet

- HS sa bai vao tap


BTVN.

Bai 49 trang 93 Sgk

Bai 49 trang 93 Sgk

- Xem lai oi xng truc . Xem trc bai mi 7. oi xng tam - HS nghe va ghi nh.

Tiet 14.8. oi xng tam

* * * * * * I/ MUC TIEU :- HS nam vng nh ngha hai iem oi xng tam (oi xng qua mot iem), hai hnh oi xng tam va khai niem hnh co tam oi xng.

- HS ve c oan thang oi xng vi mot oan thang cho trc qua mot iem cho trc, biet chng minh hai iem oi xng qua tam, biet nhan ra mot so hnh co tam oi xng trong thc te.

II/ CHUAN B :- GV : Bang phu, thc

- HS : On oi xng truc ; hoc va lam bai nha.

III. PHNG PHAP : Trc quan, van ap.IV/ HOAT ONG DAY- HOC :



1. Neu cac dau hieu nhan biet mot t giac la hnh bnh hanh (5)

2. Cho (ABC co D,E,F theo th t lan lt la trung iem AB,AC,BC (5)

- Treo bang phu ghi e. Cho HS oc e



- Cho HS nhan xet

- GV anh gia cho iem- HS oc e

- HS len bang lam

Ta co D la trung iem AB

E la trung iem AC

Suy ra DE la ng trung bnh cua (ABC

Nen DE = BC va DE//BC

Ma BF = BC

Do o DE = BF (cung bang BC)

DE // BF ( DE//BC)

Vay DEFB la hnh bnh hanh (2 canh oi song song va bang nhau)

- HS nhan xet

- HS sa bai


8. OI XNG TAM - tiet hoc trc ta a nghien cu ve phep oi xng truc va biet rang: hai oan thang, hai goc, hai tam giac oi xng vi nhau qua mot truc th bang nhau.

- Trong tiet hoc hom nay, chung ta tm hieu ve hai iem oi xng qua tam, hai hnh oi xng qua tam, hnh co tam oi xng. - HS nghe gii thieu, e y cac khai niem mi

- HS ghi ta bai

Hoat ong 3 : Hai iem oi xng qua mot iem (10)

1. Hai iem oi xng qua mot iem :

a) nh ngha : (sgk)

A va A oi xng vi nhau qua O

- Hai iem goi la oi xng nhau qua iem O neu O la trung iem cua oan thang noi hai iem o

b) Qui c : iem oi xng vi iem O qua iem O cung la iem O - Cho HS lam ?1

- Noi: A la iem oi xng vi iem A qua iem O, A la iem oi xng vi A qua O => Hai iem A va A la hai iem oi xng vi nhau qua iem O.

- Vay the nao la hai iem oi xng nhau qua O ?

- GV neu qui c nh sgk - HS thc hanh ?1

- HS nghe, hieu

- HS phat bieu nh ngha hai iem oi xng vi nhau qua iem O

- HS ghi bai

Hoat ong 4 : Hai hnh oi xng qua mot iem (10)

2. Hai hnh oi xng qua mot iem :

Hai oan thang AB va AB oi xng nhau qua iem O.

O goi la tam oi xng

nh ngha : Hai hnh goi la oi xng vi nhau qua iem O neu moi iem thuoc hnh nay oi xng vi mot iem thuoc hnh kia qua iem O va ngc lai

Lu y: Neu hai oan thang (goc, tam giac) oi xng vi nhau qua mot iem th chung bang nhau. - Hai hnh H va H khi nao th c goi la hai hnh oi xng nhau qua iem O ?

- Cho HS la ?2

- Ve iem A oi xng vi A qua O

- Ve iem B oi xng vi B qua O

- Lay iem C thuoc oan thang AB, ve iem C oi xng vi C qua O

- Dung thc e kiem nghiem rang iem C thuoc oan thang AB

- Ta noi AB va AB la hai oan thang oi xng nhau qua iem O

- The nao la hai hnh oi xng nhau qua mot iem?

- Gii thieu tam oi xng cua hai hnh (o la iem O)

- Treo bang phu (hnh 77, SGK):

- Hay ch ro tren hnh 77 cac cap oan thang, ng thang nao oi xng nhau qua O ? Giai thch ?

- GV ch dan tren hnh ve chot lai

- Neu lu y nh sgk

- Gii thieu hai hnh H va H oi xng vi nhau qua tam O - HS nghe e phan oan

- HS lam ?2

- HS neu nh ngha hai hnh oi xng vi nhau qua mot iem

- HS ghi bai

- HS quan sat, suy ngh va tra li:

+ Cac cap oan thang oi xng : AB va AB, AC va AC, BC va BC

+ Goc : BAC va BAC,

+ ng thang AC va AC

+ Tam giac ABC va tam giac ABC

- Quan sat hnh 78, nghe gii thieu

Hoat ong 5 : Hnh co tam oi xng (10)

3. Hnh co tam oi xng :

a) nh nghia :

iem O goi la tam oi xng cua hnh H neu iem oi xng vi moi iem thuoc hnh H qua iem O cung thuoc hnh H

b) nh l :

Giao iem hai ng cheo cua hnh bnh hanh la tam oi xng cau hnh bnh hanh o

- Cho HS lam ?3

- Hnh oi xng vi moi canh cua hnh bnh hanh ABCD qua O la hnh nao ?

- GV ve them hai iem M thuoc canh AB cua hnh bnh hanh

- Yeu cau HS ve M oi xng vi M qua O

- iem M oi xng vi iem M iem O cung thuoc canh hnh bnh hanh.

Ta noi iem O la tam oi xng cua hnh bnh hanh ABCD

- The nao la hnh co tam oi xng ?

- Cho HS xem lai hnh 79 : hay tm tam oi xng cua hbh ? => l

- Cho HS lam ?4

- GV ket luan trong thc te co hnh co tam oi xng, co hnh khong co tam oi xng- HS thc hien ?3

- HS ve hnh vao v

- oi xng vi AB qua O la CD

oi xng vi BC qua O la DA

- HS len bang ve

- Nghe, hieu va ghi chep bai

- Phat bieu lai nh ngha hnh co tam oi xng.

- Tam oi xng cua hnh bnh hanh la giao iem hai ng cheo

- HS lam ?4

- HS quan sat hnh ve va tra li

- HS nghe, hieu va ghi ket luan cua GV


Bai 50 trang 95 SGK

Ve iem A oi xng vi A qua B, ve iem C oi xng vi C qua B

Bai 50 trang 95 SGK

- Treo bang phu ve hnh 81

- Goi 2 HS len bang ve hnh

- HS len bang ve hnh

- HS nhan xet


BTVN.

Bai 52 trang 96 SGK

Bai 53 trang 96 SGKBai 52 trang 96 SGK

Bai 53 trang 96 SGK

- HS ghi bai tap ve nha

To duyet

BGH duyet

TUAN VIII

Tiet 15. .Luyen tap 8

* * * * * *

I/ MUC TIEU :- Van dung kien thc ve tam oi xng e chng minh hai iem , hai hnh oi xng nhau qua mot iem

II/ CHUAN B :- GV : Bang phu, thc ke, phan mau

- HS : On oi xng truc ; hoc va lam bai nha

III/ PHNG PHAP : Phan tch , am thoai, hp tac nhom.IV/ HOAT ONG DAY- HOC :



Cho hnh ve tren, MD //AB va ME//AC. Chng minh rang iem A oi xng vi iem M qua iem I- Treo bang phu ghi e

- Goi HS oc e va phan tch e


- Ca lp cung lam


- Cho HS nhan xet

- GV anh gia cho iem- HS oc e va phan tch

- HS len bang lam bai

Ta co : MD//AE (v MD//AB)

ME//AD (v ME//AC)

Vay AEMD la hnh bnh hanh (cac canh oi song song)

Ma I la trung iem cua ED

Nen I cung la trung iem cua AM

Do o A oi xng vi M qua I

- HS nhan xet

- HS sa bai (neu sai)


Bai 52 trang 96 SGK

Cho hnh bnh hanh ABCD. Goi E la iem oi xng vi D qua A, goi F la iem oi xng vi D qua iem C. Chng minh rang iem E oi xng vi iem F qua iem B


AD=AE; CD=CM

KL iem E oi xng vi

iem F qua B

Chng minh

Ta co : AE = AD (gt)

AB//CD (ABCD la hnh bnh hanh, gt)

BF = BE

Do o B la trung iem cua EF

Vay iem E oi xng vi iem F qua B

Bai 55 trang 96 SGK

Cho hnh bnh hanh ABCD, O la giao iem cua hai ng cheo. Mot ng thang i qua O cat cac canh AB va CD theo th t M va N. Chng minh rang iem M oi xng vi iem N qua O

Chng minh

Ta co ABCD la hnh bnh hanh

=> AB//CD va OA= OC

=> (so le trong)

Xet (NOC va (MOA ta co :

OA = OC (cmt)

(oi nh)

Vay : (NOC=(MOA(g-c-g)

Suy ra : OM=ON

Nen O la trung iem cua MN

Do o M oi xng vi iem N qua OBai 52 trang 96 SGK

- Treo bang phu ghi e bai

- Cho HS oc e va phan tch e


- e bai hoi ieu g ?

- Yeu cau HS ve hnh neu GT-KL

- Muon chng minh iem E oi xng vi iem F qua B ta phai chng minh ieu g ?

- Ta da vao au e chng minh B la trung iem cua EF ?

- Do au ta co ieu o ?

- Goi HS len bang trnh bay lai

- Cho HS nhan xet

- GV hoan chnh bai lam

Bai 55 trang 96 SGK

- Treo bang phu ghi e

- Goi HS oc e va phan tch

- e bai cho ta ieu g ? yeu cau ieu g ?

- Yeu cau HS len bang ve hnh ghi GT-KL

- Cho HS chia nhom. Thi gian lam bai 5

! Muon chng minh OM=ON ta chng minh (NOC=(MOA

- Cho ai dien nhom trnh bay

- Cho nhom khac nhan xet

- GV hoan chnh bai lam - HS oc e va phan tch

- Cho hnh bnh hanh ABCD

E la iem oi xng vi D qua A F la iem oi xng vi D qua C- Chng minh rang iem E oi xng vi iem F qua iem B

- HS ve hnh ghi GT-KL

- Ta phai chng minh B la trung iem cua EF

- Ta da vao nh l ng thang i qua trung iem cua canh th nhat va song song vi canh th hai se i qua trung iem cua canh th ba

- Do AE = AD

AB//CD


Ta co : AE = AD (gt)

AB//CD (ABCD la hnh b.hanh)

BF = BE

Do o B la trung iem cua EF

Vay iem E oi xng vi iem F qua B

- HS khac nhan xet

- HS sa bai vao tap

- HS oc e vaphan tch

- e bai cho ABCD la hnh bnh hanh. O la giao iem hai ng cheo,

EMBED Equation.DSMT4

. Yeu cau chng minh iem M oi xng vi iem N qua O

- HS len bang ve hnh va ghi GT-KL

- HS suy ngh ca nhan trc khi chia nhom

Ta co ABCD la hnh bnh hanh

=> AB//CD va OA= OC

=> (so le trong)

Xet (NOC va (MOA ta co OA = OC (cmt)

(oi nh)

Vay : (NOC=(MOA(g-c-g)

Suy ra : OM=ON

Nen O la trung iem cua MN

Do o M oi xng vi iem N qua O


- Nhom khac nhan xet

- HS sa bai vao tap


Cac cau sau ung hay sai ?

a) Tam oi xng cua mot ng thang la iem bat k cua ng thang o

b) Trong tam cua mot tam giac la tam oi xng cua tam giac o

c) Hai tam giac oi xng vi nhau qua mot iem th bang nhau- Treo bang phu ghi e

- Cho HS oc e

- Yeu cau HS ng tai cho tra li

- Cho HS khac nhan xet

- GV hoan chnh- HS oc e

- HS tra li

a) ung v ng thang la vo tan

b) Sai v khi lay oi xng cac nh cua tam giac th khong thuoc tam giac

c) ung v khi oi xng qua mot iem th cac canh cua hai tam giac bang nhau nen chu vi bang nhau

- HS khac nhan xet

- HS sa bai vao tap


BTVN.

Bai 54 trang 96 SGK

Bai 55 trang 96 SGK

Bai 54 trang 96 SGK

Bai 55 trang 96 SGK

- Ve nha xem lai hnh bnh hanh. Tiet sau em thc compa e hoc bai 9. Hnh ch nhat - HS ghi nhan vao tap

- HS ve xem lai nh ngha hnh co tam oi xng

Tiet169. Hnh ch nhat* * * * * *I/ MUC TIEU :- HS nam vng nh ngha hnh ch nhat, cac tnh chat cua hnh ch nhat; nam vng cac dau hieu nhan biet hnh ch nhat, tnh chat trung tuyen ng vi canh huyen cua mot tam giac vuong.

- HS biet ve hnh ch nhat (theo nh ngha va theo tnh chat ac trng cua no), nhan biet hnh ch nhat theo dau hieu cua no, nhan biet tam giac vuong theo tnh chat ng trung tuyen thuoc canh huyen, biet cach chng minh t giac la hnh ch nhat.

II/ CHUAN B :- GV : Thc thang, compa, eke; bang phu (e kiem tra, hnh ve).

- HS : On tap hnh thang, lam bai nha; dung cu: thc thang, compa

III/PHNG PHAP : am thoai, van ap.IV/ HOAT ONG DAY- HOC :



1/ nh ngha hnh thang can va cac tnh chat cua hnh thang can. (3)

- Neu cac dau hieu nhan biet hnh thang can. (2)

2/ Phat bieu nh ngha ve hnh bnh hanh va cac tnh chat cua hnh bnh hanh. (3)

- Neu cac dau hieu nhan beit ve hnh bnh hanh (2) - Treo bang phu, neu cau hoi.

- Goi mot HS len bang tra li.

- Goi HS khac nhan xet trc khi sang khai niem tiep theo

- GV anh gia, cho iem

- GV chot lai bang cach nhac lai nh ngha, tnh chat va dau hieu nhan biet hnh thang can, hnh bnh hanh. - HS len bang tra li cau hoi

- HS khac nhan xet hoac nhac lai tng khai niem, tnh chat

- HS nghe e nh lai nh ngha, tnh chat , dau hieu nhan biet hnh thang can, hnh bnh hanh.


9. HNH CH NHAT - cac tiet hoc trc, chung ta a tm hieu ve hnh thang, hnh thang can, hnh bnh hanh

- tiet nay chung ta se tm hieu ve mot loai hnh va co tnh chat cua hnh thang can va co tnh chat cua hnh bnh hanh. o la - HS nghe e hieu rang t giac can hoc la lien quan en cac hnh a hoc.

- Chuan b tam the vao bai mi

Ghi ta bai


1. nh ngha :

Hnh ch nhat la t giac co bon goc vuong

A B

D C

T giac ABCD la hnh ch nhat

(

T nh ngha hnh ch nhat ta suy ra hnh ch nhat cung la hnh bnh hanh, cung la mot hnh thang can. - T giac co 4 goc bang nhau th moi goc bang bao nhieu o? V sao?

- GV chot lai: T giac co 4 goc vuong la hnh ch nhat=> nh ngha hnh ch nhat?

- Phat bieu nh ngha,ghi bang

- Cho HS lam ?1

T o rut nhan xet g ?- HS suy ngh tra li: Mot t giac co tong bon goc bang 3600. neu cac goc bang nhau th moi goc bang 3600 : 4 = 900

- HS suy ngh, phat bieu

- Phat bieu nhac lai, ghi vao v

- Thc hien ?1 , tra li:

(Ta co : ADDC (ABCD la hcn)

BCDC (ABCD la hcn)

=> AD//BC (cung vuong goc vi CD)

Tng t : AB//CD

Vay : ABCD la hnh bnh hanh (cac canh oi song song)

(Ta co AB//CD (cmt)

Nen ABCD la hnh thang

Ma

Do o ABCD la hnh thang can

- HS rut ra nhan xet

Hoat ong 4 : Tm tnh chat (7)

2. Tnh chat :

- Hnh ch nhat co tat ca tnh chat cua hnh bnh hanh va hnh thang can

Trong hnh ch nhat, hai ng cheo bang nhau va cat nhau tai trung iem cua moi ng. - Hnh ch nhat va la hnh thang can, va la hnh bnh hanh . Vay em co the cho biet hnh ch nhat co nhng tnh chat nao?

- GV chot lai: Hnh ch nhat co tat ca cac tnh chat cua hnh bnh hanh va hnh thang can

- T t/c cua htcan va hbh ta co tnh chat ac trng cua hnh ch nhat nh the nao ?- HS suy ngh, tra li:

(Tnh chat hnh thang can : Hai ng cheo bang nhau.

(Tnh chat hnh bnh hanh :

+ Cac canh oi bang nhau.

+ Cac goc oi bang nhau.

+ Hai ng cheo cat nhau tai trung iem moi ng

- HS nhac lai tnh chat hnh ch nhat, ghi bai

Hoat ong 5 : Dau hieu nhan biet hnh ch nhat (12)

3. Dau hieu nhan biet hnh ch nhat :

(sgk trang 91)

A B

D C


AC = BD

KL ABCD la hnh ch nhat

Chng minhTa co ABCD la hnh bnh hanh Nen AB//CD

(1)

Ta co AB//CD, AC = BD (gt) Nen ABCD la hnh thang can

( (2)

T (1)va(2) (

Vay ABCD la hnh ch nhat- a ra bang phu gii thieu cac dau hieu nhan biet mot t giac la hnh ch nhat.

- ay thc chat la cac nh l, moi nh l co phan GT-KL cua no. Ve nha hay t ghi GT-KL va chng minh cac dau hieu nay. ay, ta chng minh dau hieu 4.

- Hay viet GT-KL cua dau hieu 4 ?

- Muon chng minh ABCD la hnh ch nhat ta ta phai c/m g?

- Gia thiet ABCD la hnh bnh hanh cho ta biet g?

- Gia thiet hai ng cheo AC va BD bang nhau cho ta biet them ieu g?

- Ket hp GT, ta co ket luan g ve t giac ABCD ?

- GV chot lai va ghi phan chng minh len bang - HS ghi nhan cac dau hieu vao v

- HS oc (nhieu lan) tng dau hieu

- HS ghi GT-KL cua dau hieu 4

HS suy ngh tra li: ta phai chng minh

- Cac canh oi song song, cac goc oi bang nhau

- Ket luan c ABCD la hnh thang can

- Ket hp ta suy ra c ABCD co 4 goc bang nhau

- HS ghi bai

Hoat ong 7 : Ap dung (9)

4. Ap dung vao tam giac vuong nh l :

1. Trong tam giac vuong, ng trung tuyen ng vi canh huyen bang na canh hyen .

2. Neu mot tam giac co ng trung tuyen ng vi mot canh bang na canh ay th tam giac o la tam giac vuong. - Treo bang phu ve hnh 86 len bang. Cho HS la ?3

- Lan lt neu tng cau hoi

- Cho HS tham gia nhan xet

- GV chot lai van e

- Treo bang phu ve hnh 87 len bang . Cho HS lam ?4

- Lan lt neu tng cau hoi

- Cho HS tham gia nhan xet

- GV chot lai van e - HS quan sat suy ngh

Tra li cau hoi

a) T giac ABCD co 2 ng cheo cat nhau tai trung iem moi ng nen la hnh bnh hanh

Hnh bnh hanh ABCD co nen la hnh ch nhat

b) ABCD la hnh ch nhat

Nen AD = BC

Ma AM = AD

( AM = BC

c) T o ta co the phat bieu:

Trong tam giac vuong ng trung tuyen ng vi canh huyen bang na canh huyen.

- HS khac nhan xet

- HS quan sat suy ngh

- HS quan sat, tra li tai cho :

a) ABCD la hnh ch nhat v la hnh bnh hanh co hai ng cheo bang nhau

b) Tam giac ABC vuong tai A

c) Neu mot tam giac co ng trung tuyen ng vi mot canh bang na canh ay th tam giac o la tam giac vuong.

- HS khac nhan xet

- HS ghi nh l va nhac lai

Hoat ong 9 :Cung co- Dan do (3)

BTVN.

Bai 59 trang 99 SGK

Bai 60 trang 99 SGKBai 61trang 99 SGK-Yeu cau hoc sinh nhac lai noi dung chnh trong bai.Bai 59 trang 99 SGK

Bai 60 trang 99 SGK

Bai 61 trang 99 SGK

- Hoc bai : thuoc nh ngha, cac tnh chat, cac dau hieu nhan biet hnh ch nhat.

- Chng minh cac dau hieu 1, 2, 3.

- Tiet sau Luyen tap 9- HS ve xem lai cach chng minh mot t giac la hnh ch nhat


To duyet

BGH duyet

TUAN IX

Tiet 17.Luyen tap 9.* * * * * *I/ MUC TIEU :

- Cung co phan ly thuyet a hoc ve nh ngha, tnh chat cua hnh ch nhat, cac dau hieu nhan biet ve hnh ch nhat, tnh chat cua ng trung tuyen ng vi canh huyen cua tam giac vuong, dau hieu nhan biet mot tam giac vuong theo o dai trung tuyen ng vi mot canh bang na canh ay.

- Ren luyen ky nang chng minh hnh hoc : Chng minh mot t giac la mot hnh ch nhat.

II/ CHUAN B :- GV : Thc, eke, compa, bang phu.

- HS : Hoc ly thuyet hnh ch nhat, lam bai tap ve nha.

III/ PHNG PHAP : Van ap , hp tac nhom .

IV/ HOAT ONG DAY- HOC :NOI DUNG HOAT ONG CUA GV HOAT ONG CUA HS


1/ Phat bieu nh ngha, tnh chat cua hnh ch nhat. (4)

2/ Cac cau sau ung hay sai :(6)

a) Hnh thang can co mot goc vuong la hnh ch nhat.

b) Hnh bnh hanh co mot goc vuong la hnh ch nhat.

c) T giac co hai ng cheo bang nhau la hnh ch nhat.

d) Hnh bnh hanh co hai ng cheo bang nhau la hnh ch nhat.

e) T giac co ba goc vuong la hcn

f) Hnh thang co hai ng cheo bang nhau la hnh ch nhat. - Treo bang phu ghi e

- Goi mot HS len bang

- Ca lp cung lam

- Kiem tra v bai tap vai HS

- Cho HS nhan xet cau tra li va bai lam bang

- anh gia cho iem

- GV nhac lai nh ngha, tnh chat cua hnh ch nhat va giai thch ro s ung, sai cua tng cau trong cau 2 - HS oc yeu cau e kiem tra

- Mot HS len bang tra li va lam bai (co the ve hnh e giai thch s ung sai cua moi cau)

1/ Phat bieu nh SGK trang 97

2/ Cac cau ung : a), b), d), e)

Cac cau sai: c), f)

- Tham gia nhan xet cau tra li va bai lam tren bang

- T sa sai (neu co)


Bai 63 trang 100 SGK Tm x trong cac hnh sau :

GT ABCD la hnh thang vuong

AB = 10; BC = 13; CD = 15

KL Tnh AD = ?

Ta co :

Nen ABCD la hnh ch nhat

Suy ra : AB = DH = 10 ; AD = BH

Do o : HC = DC DH

= 15 10 = 5

Ap dung nh l Phytharo vao (BCH :

BC2 = BH2 + HC2BH2 = BC2 HC2

BH2 = 132 52BH2 = 169 25 = 144

BH =12

=> AD = 12

Bai 65 trang 100 SGKT giac ABCD co hai ng cheo vuong goc nhau . Goi E, F, G , H theo th t la trung iem cua cac canh AB, BC, CD, DA. T giac EFGH la hnh g ?V sao ? GT T giac ABCD ; ACBD EA = EB ; FB = FC

GC = GD ; HA = HD

KL T giac EFGH la hnh g ?

V sao ?

Chng minh

Ta co : E la trung iem AB (gt)

F la trung iem BC (gt)

Nen : EF la ng trung bnh cua (ABC

=> EF // AC va EF = ACTng t : HG la ng trung bnh cua(ADC

=> HG // AC va HG = ACDo o : HG // EF va HG = EF

Nen : EFGH la hnh bnh hanh (co 2 canh oi ssong va bg nhau)

Ta lai co : EF // AC (cmt)

ACBD (gt)

=> EFBD

Ma EH // BD (EH la ng trung bnh cua (ABD)=> EFEH=>

Vay : Hnh bnh hanh EFGH la hnh ch nhat (co 1 goc vuong)Bai 63 trang 100 SGK

- Treo bang phu ghi e

- Yeu cau HS phan tch e


- e bai yeu cau tm ieu g ?

- Yeu cau HS neu GT-KL

- Hng dan ke BHCD

- T giac ABHD la hnh g ?

V sao ?

- T o ta co ieu g ?

- Muon tnh AD ta phai tnh oan nao ?

- Muon tnh c BH ta phai lam sao ?

- Trong tam giac vuong BHC ta biet c o dai may oan ?- Ap dung nh l Phytharo ta co ieu g ?

- Vay AD bang ?


- Cho HS khac nhan xet

- GV hoan chnh bai lam

Bai 65 trang 100 SGK- Treo bang phu ghi e


- e bai yeu cau ieu g ?

- Hng dan ve hnh

- Yeu cau HS neu GT-KL

- D oan EFGH la hnh g ?

- Khi noi ti trung iem th ta lien he en ieu g a hoc ?

- EF la g cua (ABC ?

- Ta suy ra ieu g ?

- Tng t oi vi HG

- Ta suy ra ieu g ?

- T hai ieu tren ta co ieu g?

- Vay EFGH la hnh g ?

- EFGH con thieu ieu kien g e la hnh ch nhat ?

- Ta co EF // AC va ACBD th suy ra c ieu g ?- Ma EH nh the nao vi BD ?

- Ta suy ra ieu g ?

- Nen goc HEF bang ?

- Vay hnh bnh hanh EFGH la hnh g ?

- Cho HS chia nhom . Thi gian lam bai 5

- Cho ai dien nhom len bang trnh bay

- Cho HS nhom khac nhan xet

- GV hoan chnh bai lam- HS quan sat hnh ve

- HS phan tch e

- ABCD la hnh thang vuong

AB = 10 ; BC = 13 ; CD = 15

- Tm AD

- HS len bang neu GT-KL

- HS ve theo hng dan cua GV

- ABHD la hnh ch nhat v co 3 goc vuong

- AB = DH = 10 ; AD = BH

- Muon tnh AD ta phai tnh c oan BH

- Ta da vao nh l Phytharo vao tam giac vuong BHC

- BC = 13

HC = DC DH = 15 -10 =5

BC2 = BH2 + HC2BH2 = BC2 HC2

BH2 = 132 52BH2 = 169 25 = 144

BH =12

- AD = 12

- HS len bang trnh bay lai

- HS khac nhan xet

- HS sa bai vao tap

- HS oc e va phan tch

- ACBD . E, F, G , H theo th t la trung iem cua cac canh AB, BC, CD, DA.- EFGH la hnh g ? V sao ?- HS ve hnh theo hng dan

- HS neu GT-KL

- EFGH la hnh ch nhat

- Khi noi en trung iem ta lien he en ng trung bnh

- EF la g trung bnh cua (ABC- EF // AC va EF = AC

- HG la g trung bnh cua(ADC- HG // AC va HG = AC

- HG // EF va HG = EF

- EFGH la hnh bnh hanh

- Thieu 1 goc vuong

- EFBD- EH // BD

=> EFEH-

- Hnh bnh hanh EFGH la hnh ch nhat

- HS suy ngh ca nhan sau o chia 4 nhom hoat ong

- ai dien nhom len bang trnh bay

- HS nhom khac nhan xet

- HS sa bai vao tap


BTVN.

Bai 62 trang 100 SGKBai 64 trang 100 SGKBai 66 trang 100 SGKGV. Chot lai kien thc c ban cua tiet hoc.

Bai 62 trang 100 SGKBai 64 trang 100 SGKBai 66 trang 100 SGK

- HS nghe dan va ghi chu vao tap

Tiet 18

10. ng thang song songvi mot ng thang cho trcI/ MUC TIEU :

- HS hieu c cac khai niem: Khoang cach t mot iem en mot ng thang, khoang cach gia hai ng thang song song, cac ng thang song song cach eu; hieu c tnh chat cua cac iem cach eu mot ng thang cho trc; nam vng noi dung hai nh l ve cac ng thang song song cach eu.

- HS biet cach ve cac ng thang song song cach eu theo mot khoang cach cho trc bang cach phoi hp hai eke; van dung cac nh l ve ng thang song song cach eu e chng minh cac oan thang bang nhau.

II/ CHUAN B :- GV : thc thang, eke, compa, phan mau, bang phu.

- HS : On hnh bnh hanh, hnh ch nhat; lam bai tap nha.

III/ PHNG PHAP : Qui nap am thoai , hp tac nhom




a A B

b

H K

Cho a//b. Goi A, B la 2 iem bat k thuoc a. ke AH va BK cung vuong goc vi b

a) Ch

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HH 8 Chuan KTKN