dai so 8 3 cot cuc hot

Ngy son: 27/8/04

Gio n: i S 8 Nm hc 2011 - 2012

Tun: Ngy son: Ngy dy:

Lp:

Tit :1 Chng 1: PHP NHN V PHP CHIA CAC A THC1 NHN N THC VI A THCI / MC TIU:

- Kin thc: HS nm c quy tc nhn n thc vi a thc.- K nng: K nng thu gn n thc nhanh khi lm bi tp.Bit vn dng quy tc linh hot gii ton.

- Thi : Rn luyn tnh cn thn, chnh xc trong tnh ton.

II / CHUN B:

-Thy: Gio n, phn mu.

-HS : n php nhn phn phi vi php cng n thc, a thc . III/ TIN TRNH TIT DY:1. n nh:GV nm s s, tnh hnh hc tp v cn b lp.

2. Kim tra:GV kim tra dng hc tp ca HS. Nu mt s yu cu phc v cho vic hc Ton lp 8.

3. Bi mi:

Hot ng ca ThyHot ng ca TrGhi bng

Gii thieu bai mi

GV gii thiu s lc v chng trnh i s 8.

Cho HS nhc li:

+Quy tc nhn mt s vi mt tng, ghi di dng cng thc(GV ghi gc bng).

+Quy tc nhn hai lu tha cng c s: xm.xn = ?

+Quy tc nhn cc n thc?

Mun nhn mt n thc vi a thc ta lm th no? GV gii thiu bi mi.+HS tr li:....

a(b+c) = ab+ac

+ HS tr li:...

xm.xn = xm+n

+ HS tr li...

Qui tac+Cho HS lm ?1

-Hy cho mt v d v n thc?

-Hy cho mt v d v a thc?

-Hy nhn n thc vi tng hng t ca a thc?

-Hy cng cc kt qu tm c.

(Gi HS tr li ming,GV ghi bng ng thi hng dn cch ghi.

+Qua bi tp trn, cho bit: mun nhn mt n thc vi mt a thc ta lm th no?

-GV gii thiu quy tc.

- Gi HS nhc li.HS thc hin, chng hn:

+n thc: 3x.

+a thc: 2x2-2x+5.

+HS thc hin: nhn....., cng... c kt qu:

3x(2x2-2x+5) = =3x.2x2+3x.(-2x)+3x.5

=6x3-6x2+15

+HS tr li...

HS nhc li quy tc.1/Quy tc:

?1: (SGK)

* Quy tc : (SGK T4)

p dng

+Hy p dng quy tc tnh tch sau: (-5x2) (2x3- x + )

-Gi mt i din ln bng

-GV kim tra vi nhm

-Gi HS nhn xt-HS thc hin nhm.

-Mt i din nhm ln bng

Cc nhm nhn xt bi gii2/p dng:

V d: lm tnh nhn:

(-5x2)(2x3- x + )

=(-5x2)2x3+(-5x2) (-x) +(-5x2)

= -10x5+5x3-2x2

+GV: Da vo nh ngha a thc v bi tp trn,ta c th din t ni dung quy tc trn nh sau:

A.(B+C) = A.B +A.C

+Cho hc sinh lm ?2

-Gi HS nhn dng biu thc.

-Ta thc hin nhn nh th no?

- Cho 1 HS ln bng lm

+GV xem mt s bi lm ca HS sau nhn xt v sa sai (nu c) (kq:18x4y4-3x3y3+x2y4)+GV lu : cch nhn n thc vi a thc v nhn a thc vi n thc l nh nhau. Ta c:

A.(B+C) = (B+C).A

+Cho hc sinh lm ?3-Gi HS c .

-Gi HS thc hin yu cu 1 (nu HS khng thc hin c, cho HS nhc li cng thc tnh S hnh thang)

-Gi HS thc hin yu cu tip theo.

+GV: Bi tp ?3 c dng tnh gi tr ca biu thc.

Ta thc hin th no?

- HS: lng nghe

-HS:... nhn n thc vi a thc

-HS:...s dng tnh cht giao hon ca php nhn, nh vy ta nhn n thc vi a thc

-HS ln bng lm:

-HS nhn xt:...

-HS: c .

a) Din tch mnh vn c tnh theo x v y nh sau:

S=

= (8x+3+y).y

S = 8xy+3y+y2

b) Nu x = 3 m; y = 2 m th S ca mnh vn l:

8.3.2+3.2+22=...= 58(m2)

-HS tr li:...Vit biu thc, p dng nhn n thc vi a thc, ri thu gn.

* Thay Gi tr ca x v y vo biu thc thu gn ri tnh

?2: (SGK)

?3: (SGK)

4. Cng c:

Hot ng ca ThyHot ng ca TrGhi bng

+GV cho HS lm 1c (SGK)

+GV cho HS lm bi 3a(SGK)

Hng dn: thc hin php nhn, thu ri ri tm x.

-Gi HS ln bng.

-GV nhn xt , sa sai.- HS ln bng thc hin:

- HS ln bng thc hin3x(12x 4) 9x(4x 3) = 3036x2 12x 36x2 + 27x = 30

15x = 30

x = 2* BT1C (SGK t5)

* BT3a (SGK t5)

5. Hng dn t hc : - Hc thuc quy tc. - Gii cc bi tp: 4, 5, 6 (SGK)

- BTLT: Tnh gia tr cua bieu thc:P(x)= x7-80x6+80x5-80x4+.+80x+ 15 vi x =79

IV/ RT KINH NGHIM TIT DY :..........................................................................................................................................................................................................................................................................................................................

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Tun: Ngy son:

Ngy dy:

Lp: Tit 2 2 NHN A THC VI A THC I. MC TIU: - Kin thc: HS nm vng quy tc nhn a thc vi a thc .- K nng: HS bit trnh by php nhn a thc theo cc cch khc nhau.HS c pht trin t duy, nng lc khi qut ha.

- Thi : HS c rn luyn tnh cn thn, chnh xc, kin tr, vt kh.

II. CHUN B:

-Thy: Gio n, bng ph ghi bi, ghi cc bc nhn a thc v ghi ?3. -HS: n quy tc nhn n thc vi a thc, gii bi tp v nh.

dng hc tp.III. TIN TRNH TIT DY:1. n nh: Nm s s HS, n nh lp.2. Kim tra bi c: Hot ng ca ThyHot ng ca Tr

GV gi 1 HS ln bng ?

-Pht biu quy tc nhn n thc vi a thc.

- p dng gii bi tp 1 a(kq: a) 5x5-x3-x2- GV nhn xt bi lm ca HS v cho im.1 HS ln bng:- Pht biu quy tc nh SGK

- p dng

3. Bi mi: GV gii thiu bi: tit hc trc ta bit cch nhn n thc vi a thc vy cn nhn a thc vi a thc th phi lm th no ta s cng nhau nghin cu Quy tc nhn trong tit hc ny.

Hot ng ca ThyHot ng ca TrNi dung bi

Quy tac+GV hng dn HS thc hin v d:

Cho hai a thc x-2 v 5x2+2x-1

-Hy nhn mi hng t ca a thc x-2 vi tng hng t ca a thc 5x2+2x-1

(thc hin 2 bc)

-Hy cng cc kt qu tm c

GV nhc nh HS ch du ca cc hng t

+GV: Ta ni a thc 5x3-8x2-5x+2 l tch ca a thc x-2 v a thc 5x2+2x-1

-Qua v d trn, hy cho bit mun nhn a thc vi a thc ta lm th no? Ri GV gii thiu quy tc.

-Gi HS nhc li quy tc.

-GV lu HS tch ca hai a thc l mt a thc .

+ Cho HS lm ?1

- GV gi 1 HS ln bng trnh by v xem vi bi lm ca HS cn li, sau nhn xt v sa sai nu c.

-GV lu HS c th rt bt bc nhn mi hng t ca a thc th nht vi a thc th hai

+ GV gii thiu phn ch :

-GV a bng ph ghi php ton trn bng v hng dn HS thc hin nhn hai a thc sp xp.

-Em no c th pht biu cch nhan 2 a thc qua v d trn?

-GV: y chnh l cch nhn hai a thc sp xp.

-Cho HS nhc li cch trnh bi theo SGKHS lng nghe v lm theo hng dn ca GV

-C lp cng thc hin.

-HS ng ti ch tr li ming.

-Mt HS tr li ming

-HS tr li:...

-Hai HS nhc li quy tc.

-HS ln bng trnh by:

-HS tr li:...

-

HS c SGK:...

1/Quy tc:

a)V d:

(x-2) (5x2+2x-1)

= x(5x2+2x-1)-

-2(5x2+2x-1)

=5x3+2x2-x-10x2-4x + 2

=5x3-8x2-5x+2.

b)Quy tc:

(xem SGK trg 7)

* NX: (SGK)

?1 (SGK t7)

*Ch : Khi nhn cc a thc mt bin ta sp xp a thc theo lu tha gim ca bin ri thc hin theo ct dc.

-Cch thc hin:

(Xem SGKtrg 7)

Ap dung

+Cho HS lm ?2.

-Cho HS gii bi theo nhm, yu cu gii cu a) theo 2 cch, mi dy thc hin 1 cch.

-Gi 2 i din ln bng, GV kim tra mt s nhm.

-Cho HS nhn xt, sa sai.

-Cho HS gii bi b)

*Lu HS bi ny a thc cha nhiu bin, nn khng nn tnh theo ct dc.

-Gi 1HS ln bng

-GV kim tra mt s nhm. Cho HS nhn xt, sa sai.

+Cho HS lm ?3

-Gi HS c .

-Gi HS vit biu thc tnh S hnh ch nht

*GV lu HS thu gn biu thc.

-Gi 1 HS tnh S khi:

x = 2,5m v y = 1m.

*GV lu , nn vit x = 2,5 = khi thay vo tnh s n gin hn.-HS thc hin theo nhm.

-2 i din ln bng gii cu a theo 2 cch.

-HS nhn xt bi lm ca bn.

-HS lm bi vo v.

-HS ln bng thc hin.

-HS nhn xt bi lm ca bn.

-HS ln bng thc hin.

a)Biu thc tnh S hnh ch nht l:

(2x+y) (2x-y)

=...

= 4x2-y2

b) Khi x = 2,5m v y = 1m th S hnh ch nht l:

4.()2-12=25-1 =24m2.2/ p dng:

?2: (SGK)

-Lm tnh nhn:

a)(x+3)(x2+3x-5)

=...

= x3+6x2+4x-15

b) (xy-1) (xy+5)

= ...

= x2y2+4xy-5.

-Thc hin ?3

4. Cng c:Hot ng ca ThyHot ng ca TrNi dung bi

Cng c:

Cho HS lm bi tp 7

-GV sa sai, trnh by bi gii hon chnh.

-HS lm bi.-HS lm bi vo v.

(kq:7a) x3- 3x2+3x -1 7b) x4+7x3-11x2

+6x-5

kt qu suy t cu b)

x4-7x3+11x2-6x+5.

5. Hng dn t hc Hot ng ca ThyHot ng ca TrNi dung bi

Thc hin theo quy tcHS lng nghe v ghi vo v BT8

Ta thc hin php nhn sau thu gn ri th tng gi tr vo tnh (c th s dng my tnh b ti)BT9 SGK/8

- GV hi: Gi tr ca biu thc ko ph thuc vo gi tr ca bin khi no ?HS: Khi ta thu gn khng cn bin baBT11 SGK/8

GV: Vy ta phi lm th noHS: Ta thc hin php nhn ri thu gn nu khng cn bin x na th ta chng minh xong

Chun b chu o tit ti luyn tp

IV: RT KINH NGHIM TIT DY :

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Tun:

Ngy son:

Ngy dy:

Lp:

Tit 3

LUYN TP

I MC TIU:- Kin thc: Cng c, khc su kin thc v cc quy tc nhn n thc vi a thc, nhn a thc vi a thc.- K nng: HS thc hin thnh tho php nhn n thc, a thc;bit vn dng linh hot vo tng tnh hung c th.

- Thi : Rn luyn tnh cn thn khi lm ton nhnII. CHUN B:

- Thy: Hnh v sn, phn mu.

- HS: Bi tp v nh, dng hc tp.

III. TIN TRNH TIT DY:

1) n nh: n nh, nm s s HS

2). Kim tra:

Hot ng ca ThyHot ng ca Tr

GV: Gi 2 HS ln bng lm BT 8/8 SGK cu a,b

- Cho HS nhn xt bi lm ca bn.

- Cho HS pht biu hai quy tc (nhn n thc vi a thc, nhn a thc vi a thc)

- GV nhn mnh cc sai lm thng gp ca HS nh du, thc hin xong khng rt gn . . .

- Cui cng GV nhn xt v cho im.HS1:

HS2:

(x2 xy + y2)(x + y) = x3 + x2y x2y xy2 + xy2 + y3 = x3 + y3

3) T chc luyn tp:Hot ng ca ThyHot ng ca TrNi dung bi

+Cho HS gii bi 10

.Gi hai HS ln bng gii cc bi tp 10a) v 10b)

.Cho HS nhn xt

.GV nhn mnh cc sai lm thng gp nh du, thc hin xong khng rt gn...- 2 HS ln bng trnh by.

- HS cn li lm bi vo tp v theo di bn lm nhn xt.

a/ )(x2-2x+3)(1/2x-5)

= 1/2x3-5x2-x2+10x+3/2x-15

= 1/2x3-6x2+x-15

b/ (x2-2xy+y2)(x-y)

= x3-x2y-2x2y+2xy2+xy2-y3= x3-3x2y+3xy2-y3Bi 10/8.

.Thc hin php tnh:

a)(x2-2x+3)(1/2x-5)

=...

=1/2x3-6x2+x-15

b) (x2-2xy+y2)(x-y)

=...

=x3-3x2y+3xy2-y3

+Cho HS gii bi 11

.Hy nu cch gii bi ton: CM gi tr ca biu thc khng ph thuc vo gi tr ca bin?

(Lu HS ta gp lp 7)

.Gi 1 HS ln bng, c lp lm vo v.

Cho HS nhn xt, GV sa sai .

-Nhn mnh: p dng cc quy tc nhn n thc, a thc ri thu gn biu thc, kt qu thu.HS tr li:...

...kt qu sau khi rt gn khng cn cha bin.

.Gi 1 HS ln bng, c lp lm vo v.

(x-5)(2x+3)-2x(x-3) +x+7

= 2x2+3x-10x-15-2x2+6x+x+7

= 8

HS nhn xt bi lm ca bnBi 11/8

Ta c:

(x-5)(2x+3)-2x(x-3) +x+7

=...

=-8

Vy gi tr biu thc cho khng ph thuc vo gi tr ca bin.

Cho HS lm bi 14/8 sgk.

c .

-Hy vit dng tng qut ca 3 s chn lin tip?

(HS thng qun a thuc N, GV b sung).

-Hy vit BTS ch mi quan h tch hai s sau ln hn hai s u l 192 ?

-GV: Tm c a, ta s tm c 3 s cn tm , hy tm a ?

-Gi HS nhn xt bi lm ca bn.

-Vy 3 s cn tm l nhng s no?-HS c .

-HS tr li...

..2a, 2a+2, 2a+4 vi a thuc N

-HS lm bi vo v, 1HS tr li....

(2a+2)(2a+4)- 2a(2a+2)=192

-1HS ln bng, c lp lm bi vo v.

4a2+8a+4a+8-4a2-4a=192

8a = 184

a = 23

-HS nhn xt...

-HS l cc s 46, 48, 50.Bi 14 trang8:

+ Gi 3 s chng lin tip l 2a, 2a + 2, 2a+4 vi a N

Ta c:(2a+2)(2a+4)- 2a(2a+2)=192

.....

a+1=24

a =23

Vy ba s l 46, 48, 50.

Cho HS lm bi 12/8.

-HS lm bi trn phiu hc tp.

-GV thu mt s bi lm trn ca HS chm.

-GVnhn xt, sa sai (nu c).

-Hy nu cc bc gii bi ton Tnh gi tr biu thc khi bit gi tr ca bin?

-HS lm bi trn phiu .

HS:...gm 2 bc:

- Thu gn biu thc

-Thay gi tr ca bin vo BT ri tnhBi 12/8

4. Cng c:Nhn xt tnh hnh hc tp qua tit dy, lu mt s sai lm ca HS thng mt phi.

5. Dn d : Hot ng ca ThyHot ng ca TrNi dung bi

Ta thc hin php nhn sau thu ri ri tm xHS lng nghe v ghi vo vBi tp 13 SGK/9

Ta thc hin php nhn theo quy tcBi tp 15 SGK/9

c trc bi 3 Nhng hng ng thc ng nh sau xem KQ ca bi 15 v NX

IV.RT KINH NGHIM TIT DY:..........................................................................................................................................................................................................................................................................................................................

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Tun:

Ngy son :

Ngy dy:

Lp:Tit 4

3 NHNG HNG NG THC NG NH

I. MC TIU:

- Kin thc: HS nm c cc hng ng thc: bnh phng ca mt tng, bnh phng ca mt hiu, hiu hai bnh phng.

- K nng: Bit vn dng cc hng ng thc trn gii mt s bi tp n gin, vn dng linh hot tnh nhanh nhm.

- Thi : Rn luyn kh nng quan st, nhn xt ng v chnh xc.

II.CHUN B:

Thy: Gio n, SGK, bng ph ghi 3 hng ng thc, bng ph ghi bi, v hnh 1 SGK/9 HS : BTVN. dng hc tp. n li bi c. Xem trc bi mi.III.TIN TRNH TIT DY:

1. n nh: Nm s s lp.2. Kim tra bi c :

Hot ng ca ThyHot ng ca Tr

HS1: -Hy pht biu quy tc nhn hai a thc?

-Gii bi tp 15a).(SGK)

HS1: - Pht biu nh SGK

HS2: -Gii bi tp 15b)

-Tnh (a-b) (a+b) vi a,b l hai s bt k.

HS2:

3. Bi mi:

Gii thiu bi: - Khng thc hin php nhn c th tnh tch trn mt cch nhanh chng hn khng?

Hot ng ca ThyHot ng ca Tr Ni dung bi

Bnh phng cua mot tong.

+HS lm ?1

-Cho HS tnh (a+b) (a+b)

-Rt ra (a+b)2=?

+GV gii thiu tng qut vi A, B l cc biu thc tu :

(A+B)2=A2+2AB+B2.(ghi bng) v gii thiu tn gi Hng ng thc.

-GV dng tranh v sn (H1-SGK),hng dn HS nm c ngha hnh hc ca cng thc.

-HS lm ?2

-Quay li BT 15

.Xc nh dng,cc biu thc A,B.

.i chiu kt qu?

+GV cho HS lm phn p dng.

-Gi HS ng ti ch c kt qu bi a). Yu cu gii thch cch lm.

-Cho HS lm bi b,c trn phiu hc tp.

-GV gi 2 HS ln bng thc hin, kim tra mt s em.

-Cho HS nhn xt, GV sa sai (nu c).

-GV gi 2 HS ln bng thc hin, kim tra mt s em.

-Cho HS nhn xt, GV sa sai (nu c).-HS thc hin:

(a+b)(a+b)=.....

=a2+2ab+b2.

-HS:

(a+b)2=a2+2ab+b2-HS Pht biu bng li:...

-HS: Bi 15a) c dng (A+B)2 vi A=1/2x; B=y.

.HS i chiu kt qu.

-HS tr li:...

.2HS ln bng. HS thc hin trn phiu hc tp.

.HS nhn xt...

.2HS ln bng...

.HS nhn xt...1.Bnh phng ca mt tng:

Vi A,B tu , ta c:

(A+B)2=A2+2AB+B2*.p dng:

a) Tnh:

(a+1)2=... =a2+2a+1

b) x2+4x+4

=... =(x+2)2c) 512=(50+1)2 =502+2.50+1

=2601

3012=(300+1)2

=3002+2.300+1

=90601

Bnh phng cua mot hieu

+Hy vn dng HT trn tnh:

[A+(-B)]2.

*GV lu HS:

[A+(-B)]2 =(A-B)2

-GV gii thiu hng ng thc, cch gi tn .

*GV: ta cng c th tm(A-B)2 bng cch tnh (A-B)(A-B) hy t thc hin theo cch ny v kim tra.

+Cho HS lm ?4.

+Cho HS lm phn p dng.

.Gi 2 HS tnh 2 cu a,b.C lp theo di nhn xt.

.Yu cu HS gii thch cch thc hin cc bi tp trn.

.Gi 1 HS tnh cu c.-HS thc hin:

...=A2-2AB+B2-HS pht biu bng li...

.2HS thc hin trn bng.

.HS nhn xt...

-1HS ln bng, c lp lm vo v, nhn xt.2.Bnh phng ca mt hiu:

Vi A,B tu , ta c:

(A-B)2=A2-2AB+B2+p dng:

a) Tnh:

(x-1/2)2=x2-2.x.1/2+

+(1/2)2=x2-x+1/4

b) (2x-3y)2=

=(2x)2-2.2x.3y+(3y)2 =4x2-12xy+9y2```

Hiu ca hai lp phng:

+Cho HS xem li kt qu bi tp kim tra ming, rt ra:

a2-b2=(a+b)(a-b) .GV gii thiu tng qut vi Av B l cc biu thc tu .

-GV ghi HT ln bng v gii thiu tn gi.

+Cho HS lm ?6.

+Cho HS lm phn p dng.

-Gi 2HS lm cc bi a,b.Yu cu gii thch cch lm, xc nh A,B.

-C lp tnh nhanh cu c) .GV gi HS c kt qu v gii thch cch tnh.

-Cho HS quan st bi ?7 trn bn ph.

Gi HS ng ti ch tr li.

-GV cht li cc HT va hc v cc vn dng ca n vo vic gii bi tp.-HS pht biu bng li...

-HS lm bi v nhp.

.1HS tr li ming.

-HS tr li

.c v Th ng

.Sn rt ra c HT:

(A-B)2=(B-A)23) Hiu ca hai lp phng:

Vi A,B tu , ta c:

A2-B2=(A+B)(A-B)

+p dng:

a) Tnh:

(x+1)(x-1)=x2-1.

(x-2y)(x+2y)

=x2-(2y)2=x2-4y2c) Tnh nhanh:

56.64=(60-4)(60+4)

=602-42 =3600-16

=3584

4. Cng c:


- GV yu cu

* Gi :

1/ c v Th ai ng?

2/ Sn rt ra c HT?

- Cho HS lm cc bi tp Sgk (tr11)

* Gi : xc nh gi tr ca A,B bng cch xem A2 = ? ( A

B2 = ? (B

Yu cu HS nhn xt- HS c ?7 (sgk trang 11)

- Tr li ming:

- Kt lun:

(x y)2 = (y x)2- HS hp tc lm bi theo nhm

- Mi em t trnh by bi lm ca mnh

16b/ 9x2 +y2 +6xy = (3x +y)2

c/ 25a2+4b220ab = (5a-2b)2 - Nhn xt bi lm ca bnBi tp ?7

+ C c v Th u ng

+ HT : (A-B)2 = (B-A)2

Bi Tp 16(bc),

16b/ 9x2 +y2 +6xy = (3x +y)2

c/ 25a2+4b220ab = (5a-2b)2

5. Dn d : -Hc thuc cc hng ng thc 1,2,3


- Hc thuc lng hng ng thc ch du ca hng ng thc

- Bi tp 16 trang 8 Sgk

* p dng HT 1+2- HS nghe dnBi tp 16 trang 11 Sgk


* VT: p dng HT 1

VP: Nhn n thc vi a thc

(A + B)2 = A2 + 2AB + B2(A-B)2 = A2 2AB+ B2

Bi tp 17 trang 11 Sgk

IV. RT KINH NGHIM TIT DY:..........................................................................................................................................................................................................................................................................................................................

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Tun:

Ngy son :

Ngy dy:

Lp:

Tit 5

LUYN TPI. MC TIU:

- Kin thc: Cng c kin thc v cc hng ng thc : Bnh phng ca mt tng , bnh phng ca mt hiu , hiu hai bnh phng.

- K nng: HS vn dng thnh tho cc hng ng thc trn vo gii ton.

- Thi : Pht trin t duy logic , thao tc phn tch , tng hp.

II.CHUN B:

Thy: Gio n. Phiu HT. Bng ph.

HS : n bi c + lm BTVN.

III.TIN TRNH TIT DY:

1)n nh2) Kim tra:


- Treo bng ph kim tra

- Kim v bi lm nh (3HS)

- Cho HS nhn xt

- GV nh gi cho im - Mt HS ln bng, cn li chp vo v v lm bi ti ch.

a) (x+1)2

b) (5a-2b)2

- Nhn xt bi lm bng

- T sa sai (nu c) 1/ Vit ba HT hc (6)

2/ Vit cc bthc sau di dng bnh phng 1 tng (hiu) (4)

a. x2 +2x +1

b. 25a2 +4b2 20ab

3) Luyen tap:


+Cho HS gii bi tp 16

-Gi 2 HS ln bng

-C lp theo di ,nhn xt

-GV nhn xt , sa sai (nu c)-HS1 gii bi a

-HS1gii bi d 1) Bi 16/11

a/ x2 +2x +1 = (x+1)2

d/ x2 x +1/4

=x2 2.x.1/2 + (1/2)2

=(x-1/2)2

+ Cho HS lm bi 18

-Gi 1 HS ln bng

-GV gip 1 s HS yu nhn dng hng ng thc mi bi , xc nh A v B tm c hng t phi tm

-Gi HS nu bi tng t , 1 HS khc in vo ch trng .

- GV m rng : cho cc bi.

a) ...-12xy +... = (3x- ...)2

b) .... + 3x + ....= (x+...)2

c) ... +8xy + ... = (...+...)2

. Gi HS ng ti ch tr li , GV ghi bng.

. cu c ta cn cch in no khc.-1HS ln bng

- C lp theo di nhn xt

-1HS cho , HS khc in vo ch trng

- HS tr li

HS :

c1)x2 + 8xy + 16y2=(x+4y)2 c2)4x2+8xy+4y2 =(2x+2y)22)Bi 18: Khi phc cc hng ng thc:

a) x2+6xy+...=(...+3y)2x2+6xy+9y2 =(x+3y)2

b) ...-10xy +25y2 = (...-...)2x2-10xy+25y2=(x-y)2

Bi tp thm :

Kt qu:

a)9x2-2xy+4y2=(3x-2y)2

b)x2+3x+9/4 =(x+3/2)2

+Cho HS gii bi 17

-GV ghi : CM rng :

(10a+5)2= 100a . (a+1)+25

-Hy nu cch chng minh (GV ghi bng , sa sai nu c)

-Vn dng kt qu trn tnh:

252 =? 352 =?

652 =? 852 =?

HS tr li

HS tr li nhanh

252 = 625

352 = 1225

652 = 4225

852 = 7225

3)Bi 17 :

Ta c :

100a.(a+1) +25

=100a2+100a+25

=(10a)2 +2.10a.5 +52

=(10a+5)2

+Cho HS gii bi 20

. GV ghi ng thc :

x2+2xy+4y2 =(x+2y)2. Kt qu trn l ng hay sai , gii thch

. GV lu HS : y l trng hp nhm ln m HS thng mc phi

+Cho HS gii bi 23

. GV ghi : c/minh rng :

(a+b)2 = (a-b)2 +4ab

(a-b)2= (a+b)2- 4ab

. Cho HS lm theo nhm

. Gi 2 i din ln bng gii , GV kim tra 1 s nhm

. Cho HS nhn xt , GV nh gi , sa sai(nu c)

. c/minh A=B c nhng cch no ?

-Gi HS tnh phn p dng , GV ghi bng

-Vi bi tp trn ta thy nu bit tng (hiu) v tch ta s tm c hiu (tng) ca 2 s ta s tm c 2 s cho

-Cc cng thc c c/minh trn cho ta mi lin h gia bnh phng ca 1 tng v bnh phng ca 1 hiu , sau ny cn c ng dng trong vic tnh ton , c/minh ng thc.

.Cho HS lm nhanh bi 22 trn phiu hc tp

HS suy ngh tr li

.HS hot ng nhm

. 2 i din ln bng thc hin

. HS nhn xt

. HS tr li ming

C1: Nu c 1 v phc tp , ta thu gn v phc tp

_ kt qu thu gn chnh l v n gin.

C2: Nu c

A-B=C th A=B

C3: Nu c

A=C

C=B

th A=B

.HS lm bi trn phiu hc tp

4) Bi 20 :

Cch vit :

x2+2xy+4y2=(x+2y)2l sai

V :

(x+2y)2=x2+2x2y +2y)2=x2+4xy+4y25) Bi 23:

a)Ta c :

(a-b)2+4ab

=a2-2ab+b2+4ab

=a2+2ab+b2= (a+b)2Vy(a+b)2=

(a-b)2+4ab

b)

(a+b)2 - 4ab

=a2+2ab+b2- 4ab

=.....

= (a-b)2Vy(a-b)2=

(a+b)2- 4ab

p dng

a)Vi a+b=7, a.b=12

th (a-b)2=72-4.12=1

b)Vi a-b=20,a.b=3

th (a+b)2=202+4.3=412

. GV thu , chm nhanh 1 s HS.. Kt qu:

a)1012=(100+1)2 =...=10201

b)1992=(200-1)2 =...=39601

c)47.53=(503)(50+3)

=...=2491

4. Cng c:Nu nhn xt u khuyt im ca HS qua gi luyn tp5. Dn d:


- Xem li li gii cc bi gii.


* Tch thnh bnh phng ca mt tng hoc hiu

- Bi tp 24 trang 11 Sgk* Dng HT


* Tng t bi 24(A + B)2 = A2 + 2AB + B2(A-B)2 = A2 2AB+ B2

- HS nghe dn v ghi ch vo v





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Tun:

Ngy son :

Ngy dy:

Lp:

Tit 6

4 NHNG HNG NG THC NG NH (tt)

I. MC TIU:

- Kin thc: Nm c cc hng ng thc : Lp phng ca mt tng , lp phng ca mt hiu.

- K nng: Bit vn dng cc hng ng thc trn gii bi tp

- Thi : Rn luyn k nng tnh ton , cn thn.

II.CHUN B:

Thy: Gio n. Phn mu

HS : Gii bi tp v nh. + Hc thuc cc hng ng thc

(A+B)2 , (A-B)2 , A2 B2III.TIN TRNH TIT DY:

1) n nh: 2) Kim tra bi c:

Hot ng ca thyHot ng ca trNi dung bi

- Treo bi

- Gi mt HS ln bng

- Cho HS nhn xt bng

- nh gi cho im - Mt HS ln bng

- HS cn li lm vo v bi tp

1/ = 9x2 6xy + y2

2/ = 4x2 1/ Vit 3 hng ng thc (6)

2/ Tnh :

a) (3x y)2 = (2)

b) (2x + )(2x - ) (2)

3) Bi mi:

GV vo bi trc tip: ta hc ba hng ng thc bc hai Chng ta tip tc nghin cu v cc hng ng thc bc baHot ng ca thyHot ng ca trNi dung bi

Lp phng ca 1 tng :

GV : Ta c th rt gn (a+b)(a+b)2 = (a+b)3(a+b)3 = a3+3a2b+3ab3+b3

Vi a,b l cc s tu , ng thc trn lun ng

-Ta c y l mt hng ng thc ng nh na , GV gii thiu bi mi- GV gii thiu tng qut vi A v B l cc biu thc tu ta cng c

(A+B)3 = A3+3A2B+3AB2+B3. GV gii thiu cch gi tn hng ng thc v ghi bng.

. Hy pht biu hng ng thc trn bng li

-Cho HS thc hin phn p dng

. HS lm bi vo v

. Gi 2 HS ln bng tnh . Yu cu HS trnh by cch lm sau khi gii , xc nh r A,B trong cch p dng

. GV nhn xt , sa sai (nu c)- HS pht biu bng li

- HS lm bi vo v

- 2 HS ln bng

a) A=x , B =1

b) A=2x , B =y4)Lp phng ca 1 tng :

Vi A, B tu ta c:

(A+B)3 = A3+3A2B+3AB3+B3 (4)

*p dng :

a) Tnh :

(x+1)3 = =x3+3x21+3x.13+13=x3+3x2+3x+1

b)Tnh :

(2x+y)3

= (2x)3+3.(2x)2y + 3.2x.y2+y3=8x3+12x2y+6xy2+y3

Lp phng ca mt hiu:

- Cho HS lm bi 23

Tnh [a+(-b)]3 (vi a,b l cc s tu )

. HS lm trn phiu hc tp

. Gi 1 HS ln bng thc hin , GV kim tra 1 s HS.

. Cho HS nhn xt

. Ta c : a+(-b) = a-b

(a-b)3 = ?

. GV gii thiu tng qut vi A,B tu v cch gi tn hng ng thc .

- Hy pht biu hng ng thc (5) bng li.

- Cho HS lm phn p dng

. C lp cng lm bi a,b : gi 2HS ln bng gii , yu cu trnh by cch gii , xc nh A,B.

. GV lu HS thng xc nh B sai

VD: a) B= -1/3

b) B= -2y

. HS lm trn phiu hc tp

. HS i chiu vi bi lm ca mnh v cho nhn xt.

. HS tr li ...

. HS pht biu bng li

. C lp cng lm

. 2 HS ln bng gii

a) A=x , B= 1/3

b) A=x , B= 2y5)Lp phng ca mt hiu:

Vi A,B tu , ta c

(A-B)3

= A3-3A2B+3AB2-B3 (5)

*p dng :

a)Tnh:

(x-1/3)3=x3-3.x2.1/3 +3.x.(1/3)2+(1/3)3= x3-x2+x/3+1/27

b)Tnh:

(x-2y)3=x3-3.x2.2y3 +3.x.(2y)2+(2y)3=x3-6x2y+12xy2+8y3

. HS thc hin cu c trn phiu hc tp ca nhm .

. GV kim tra kt qu ca cc nhm

. Chn 1 i din nhm trnh by bi gii ca nhm .

. Cho HS nhn xt.- HS thc hin theo nhm trn phiu h tp.

.1 i din nhm trnh by bi gii

. Cc nhm so snh kt qu ,nhn xt

Kq :

1),3) ng

2),4),5) Sai

Nhn xt:

(A-B)2 = (B-A)2(A-B)3 = -(B-A)3

4. Cng c:


. Cho HS nhc li cc HT hc

. GV lu HS v s x du trong HT (a-b)3; khc su cho HS : du m ng trc lu tha bc l ca b. HS tr li.

5. Dn dHot ng ca thyHot ng ca trNi dung bi

- Hc bi: vit cng thc bng cc ch tu , ri pht biu bng li.


* p dng hng ng thc 4,5


* Tng t bi 26

- Bi tp 28 trang 12 Sgk* Tng t bi 26- HS nghe dn v ghi ch vo v

(A+B)3= A3+3A2B+3AB2+B3(A-B)3= A3-3A2B+3AB2 -B3Bi tp 26 trang 12 Sgk




Tun:

Ngy son :

Ngy dy:

Lp:

Tit 7

5. NHNG HNG NG THC NG NH (tt)

I.MC TIU:

- Kin thc: HS nm c cc hng ng thc: Tng hai Lp phng, hiu hai lp phng.

- K nng: Bit vn dng cc hng ng thc mt cch linh hot gii bi tp.- Thi : Rn luyn tnh cn thn trong lm ton.

II. CHUN B:

Thy: Bng ph ghi bi tp, phn mu

HS: Hc thuc bi c + gii bi tp v nh


1. n nh 2. Kim tra bi c :


- Treo bi

- Gi mt HS ln bng

- Cho HS nhn xt bng

- nh gi cho im - Mt HS ln bng

- HS cn li lm vo v bi tp

1/ = 9x2 6xy + y2

2/ = 4x2 1/ Vit 3 hng ng thc (6)

2/ Tnh :

a) (3x y)2 = (2)

b) (2x + )(2x - ) (2)

3. Bi mi: GV vo bi trc tip: ta hc ba hng ng thc bc hai Chng ta tip tc nghin cu v cc hng ng thc bc ba


- Nu ?1 , yu cu HS thc hin

- T ta rt ra a3 + b3 = ?

- Vi A v B l cc biu thc tu ta c?

- Yu cu HS pht biu bng li hng ng thc

- GV pht biu cht li: Tng hai lp phng ca hai bthc bng tch ca tng hai bthc vi bnh phng thiu ca hiu hai bthc o.

- Ghi bng bi ton p dng

- GV gi HS nhn xt v hon chnh - HS thc hin ?1 cho bit kt qu:

(a + b)(a2 ab + b2) = = a3 + b3

A3+B3= (A+B)(A2-AB+B2)

- HS pht biu bng li

- HS nghe v nhc li (vi ln)

- Hai HS ln bng lm

a) x3+8 = (x+8)(x2- 2x+ 4)

b) (x+1)(x2 x+1) = x3 + 16. Tng hai lp phng:Vi A v B l cc biu thc tu ta c:

A3+B3= (A+B)(A2-AB+B2)

Qui c gi A2 AB + B2 l bnh phng thiu ca mt hiu A B

Ap dng:

a) x3+8 = (x+8)(x2- 2x+ 4)

b) (x+1)(x2 x+1) = x3 + 1

- Nu ?3 , yu cu HS thc hin

- T ta rt ra a3 - b3 = ?

- Vi A v B l cc biu thc tu ta c?

- Ni v ghi bng qui c, yu cu - HS pht biu bng li Ht

- GV pht biu cht li: Hiu hai lp phng ca hai bthc bng tch ca hiu hai bthc vi bnh phng thiu ca tmg hai bthc o.

- Treo bng ph (bi ton p dng), gi 3HS ln bng .

- Cho HS so snh hai cng thc va hc

- GV cht li vn -HS thc hin ?3 cho bit kt qu:

(a -b)(a2 + ab + b2) = = a3 - b3

A3-B3= (A-B)(A2+AB+B2)

- HS pht biu bng li

- HS nghe v nhc li (vi ln)

- Ba HS lm bng (mi em mt bi), cn li lm vo v

a) (x 1)(x2+x+1) = x3 1

b) 8x3 y3 = (2x)3 y3

= (2x y)(4x+2xy+y2)

c) (x +2)(x2 -2x + 4) = x3 - 23

= x3 8

- Nhn xt bng sau khi lm xong

- HS suy ngh, tr li

- HS theo di v ghi nh 7. Hiu hai lp phng:

Vi A v B l cc biu thc tu ta c:

A3-B3= (A-B)(A2+AB+B2)

Qui c gi A2 + AB + B2 l bnh phng thiu ca mt tng A + B

Ap dng:

a) (x 1)(x2+x+1) = x3 1

b) 8x3 y3 = (2x)3 y3

= (2x y)(4x+2xy+y2)

c) (x +2)(x2 -2x + 4) = x3 - 23

= x3 8

A3+B3 = (A+B)(A2-AB+B2)

A3-B3 = (A -B)(A2+AB+B2)

4. Cng c:


- Gi HS ln lt nhc li by hng ng thc hc (treo bng ph v m ra ln lt)

- Khi A = x, B = 1 th cc cng thc trn c vit di dng nh th no?

- GV cht li v ghi bng - HS thay nhau nu cc hng ng thc hc

(A+B)2 = A2 + 2A + B2(A B)2 =A2 2A + B2 A2 B2= (A +B)(A -B)

(A +B)3=A3+3A2 B+3AB2+B3

(A -B)3 = A3 3A2B+3AB2 B3

A3 + B3 =(A +B)(A2 -AB +B2)

A3 B3 =(A B)(A2+AB+B2)- Ta c by hng ng thc ng nh:

(A+B)2 = A2 + 2A + B2(A B)2 =A2 2A + B2 A2 B2= (A +B)(A -B)

(A +B)3=A3+3A2 B+3AB2+B3

(A -B)3 = A3 3A2B+3AB2 B3

A3 + B3 =(A +B)(A2 -AB +B2)

A3 B3 =(A B)(A2+AB+B2)

5. Dn d:Hot ng ca thyHot ng ca trNi dung bi

- Vit mi cng thc nhiu ln.

- Din t cc hng ng thc o bng li.


* p dng hng ng thc 6,7


* Tng t bi 30

- Bi tp 32 trang 16 Sgk* Tng t bi 30- HS nghe dn

x3 + 1 = (x +1)(x2 - x +1)

x3 1 = (x 1)(x2 + x + 1)

- Ghi ch vo v Bi tp 30 trang 16 Sgk



IV. RT KINH NGHIM TIT DY:.................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Tun:

Ngy son :

Ngy dy:

Lp:

Tit 8

LUYN TP (5)I. MC TIU:

- Kin thc: Cng c kin thc v 7 hng ng thc ng nh.

- K nng: HS bit vn dng kh thnh tho cc hng ng thc ng nh vo bi ton.

- Thi : Hng dn HS cch dng hng ng thc (A ( B)2 xt gi tr ca mt s tam thc bc hai.

II. CHUN B:

Thy: Bng ph ghi bi tp, phn mu

HS: - Hc thuc lng 7 HT ng nh

- Bng nhm


1. n nh

2. Kim tra bi c :


- Treo bng ph a ra kim tra. Gi mt HS

- Thu v kim giy vi em

- Cho HS nhn xt

- Sa sai v nh gi cho im - Mt HS ln bng, cn li lm vo giy

a) 8x3 1=(2x-1)(4x2+2x+1)

b)27+64y3=(3+4y)(9-24y+16y2)

- HS c gi np giy lm bi.

- Nhn xt bi lm bng

- T sa sai (nu c). 1/ Vit cng thc tng hai lp phng, hiu hai lp phng (5)

2/ Vit cc biu thc sau di dng tch: (5)

a) 8x3 1

b) 27 + 64y3

3. Luyen tap :Hot ng ca thyHot ng ca trNi dung bi

- Ghi bi tp 31 ln bng , cho mt HS ln bng trnh by li gii, GV kim v bi lm HS

- Cho HS nhn xt li gii ca bn, sa cha sai st v cht li vn (v cch gii mt bi chng minh ng thc). - HS ln bng trnh by li gii, cn li trnh v bi lm trc mt

- HS nhn xt sa sai bi lm bng

- HS nghe ghi hiu hng gii bi ton cm ng thc Bi 31 trang 16 Sgk

a)VP: (a + b)3 3ab(a + b)

= a3 + 3a2b+ 3ab2+ b33a2b 3ab2 = a3 + b3 .

Vy :a3 + b3 = (a+b)3-3ab(a+b)

b) (a b)3 + 3ab(a-b) = a3 3a2b +3ab2 b2 = a3- b3

-Treo bng ph.Gi mt HS ln bng, yu cu c lp cng lm

- Cho vi HS trnh by kt qu, c lp nhn xt

- GV nhn xt v hon chnh- HS lm vic c nhn

- Mt HS lm bng

a) (2+xy)2 = 4 + 4xy + x2y2

b) (5 -3x)2 = 25 - 30x + 9x2

c) (5 x2)(5+ x2) = 25 x4

d) (5x 1)3=125x350x2+15x1

e)(x -2y)(x2 +2xy + 4y2)=x3- 8y3

f) (x+3)(x2-3x+9) = x3 + 27

- Trnh by kt qu c lp nhn xt, sa sai (nu c)

- T sa sai v ghi vo v Bi 33 trang 16 Sgk

a) (2+xy)2 = 4 + 4xy + x2y2

b) (5 -3x)2 = 25 - 30x + 9x2

c) (5 x2)(5+ x2) = 25 x4

d) (5x 1)3= 125x3 50x2 + 15x 1

e) (x -2y)(x2 +2xy + 4y2)=x3- 8y3

f) (x+3)(x2-3x+9) = x3 + 27

- Ghi bi 34 ln bng, cho HS lm vic theo nhm nh t pht

- Gi i din mt vi nhm nu kt qu, cch lm

- GV ghi bng kim tra kt qu - HS lm bi tp theo nhm nh cng bn

- i din nu cch lm v cho bit p s ca tng cu

- Sa sai vo bi (nu c) Bi 34 trang 17 Sgk

a) (a+b)2 (a-b)2 = = 4ab

b) (a+b)3-(a-b)3-2b3 == 6a2b

c) (x+y+z)22(x+y+z)(x+y)+(x+y)2

= = z2

- Ghi bng bi 35 ln bng

- Hi: Nhn xt xem cc php tnh ny c c im g? (cu a? cu b?)

- Hy cho bit p s ca cc php tnh. GV trnh by li - HS ghi bi vo v

- HS suy ngh tr li

a) C dng bnh phng ca mt tng

b) Bnh phng ca mt hiu

- HS lm vic c th-nu kt qu Bi 35 trang 17 Sgk

a) 342 + 662 + 68.66

= 342 + 662 + 2.34.66 = (34 + 66)2

= 1002 = 10.000

b)742 + 242 48.74

= 742 + 242 2.24.74

= (74 24)2 = 502 = 2500.

4. Cng c:


- Chia 4 nhm hot ng, thi gian (3).

- GV quan st nhc nh HS no khng tp trung

- Sau gi i din nhm trnh by

- Yu cu cc nhm nhn xt ln nhau - HS chia nhm lm bi

- Cu 1 b ng

- Cu 2 d ng

- Cu 3 b ng

-C i din nhn xt bi ca nhm khc1/ Rt gn (x+1)3-(x-1)3 ta c:

a) 2x2+2 b)2x3+6x2

c) 4x2+2 d)Kt qu khc

2/Phn tch 4x4+8x2+4 thnh tch

a)(4x+1)2 b) (x+2)2c)(2x+1)2 d) (2x+2)23/ Xt (2x2 +3y)3=4x3 + ax4y + 18x2y2 +by3. Hi a,b bng ?

a/ a=27 b=9 b)a=18 b=27

c/ a=48 b=27 d)a=36 b=27

5. Dn d:

- Hc li cc hng ng thc


* Bin i sau thay gi tr

- Bi tp 38 trang 17 Sgk* Phan tch tng v sau sosnh- Xem li tnh cht php nhn phn phi i vi php cng- HS nghe dn , ghi ch vo v

- p dng hng ng thc 1,4

- p dng 7 hng ng thcBi tp 36 trang 17 Sgk


IV. RT KINH NGHIM TIT DY:.......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

..........................................................................................................................................................................................................................................................................................................................Tun:

Ngy son :

Ngy dy:

Lp:

Tit 9

6. PHN TCH A THC THNH NHN T BNG

PHNG PHP T NHN T CHUNGI. MC TIU:

- Kin thc: HS hiu th no l phn tch a thc thnh nhn t.

- K nng: Bit cch tm nhn t chung v t nhn t chung

- Thi : Rn luyn tnh cn thn trong lm ton.

II. CHUN B:

Thy: Bng ph, ghi bi tp

Tr: Bng nhm


1. n nh

2. Kim tra bi c : Hot ng ca thyHot ng ca trNi dung bi

- Treo bng ph. Gi mt HS ln bng. C lp cng lm bi tp

- Kim tra bai tp v nh ca HS

- Cho HS nhn xt bng

- GV nh gi cho im - Mt HS ln bng vit cng thc v lm bi

- C lp lm vo v bi tp

Nhn xt, nh gi bi lm ca bn trn bng

(a+b)2 +(a b)2 = = 2a2 + 2b2 - Vit 7 ht ng nh: (7)

(x+y)2 =

(x -y)2 =

x2 y2 =

(x+y)3 =

(x y)3 =

x3 +y3 =

x3 y3 =

- Rt gn biu thc: (3)

(a+b)2 + (a b)2 =

3. Bi mi :

V: Chung ta a biet phep nhan a thc v du: (x +1)(y - 1)=xyx+y 1 thc chat la ta a bien oi ve trai thanh ve phai. Ngc lai, co the bien oi ve phai thanh ve trai?


- Nu v ghi bng v d 1

- n thc 2x2 v 4x c h s v bin no ging nhau ?

- GV cht li v ghi bng

Ni:Vic bin i nh trn gi l phn tch a thc thnh nhn t.

- Vy phn tch a thc thnh nhn t l g?

- Cch lm nh trn gi l phng php t nhn t chung

- Nu v d 2, hi: a thc ny c my hng t? Nhn t chung l g?

- Hy phn tch thnh nhn t?

- GV cht li v ghi bng bi gii

- Nu ch ly 5 lm nhn t chung ? 2x2 = 2x . x

4x = 2x . 2

- HS ghi bi vo tp

- Phn tch a thc thnh nhn t l bin i a thc thnh mt tch ca nhng a thc

- HS hiu th no l phng php t nhn t chung

- HS suy ngh tr li:

+ C ba hng t l

+ Nhn t chung l 5x

- HS phn tch ti ch

- HS ghi bi

- Cha n kt qu cui cng 1/ V d 1:

Hy phn tch a thc 2x2 4x thnh tch ca nhng a thc.

2x2-4x = 2x.x+2x.2 = 2x(x-2)

V d 2:

Phn tch a thc sau thnh nhn t 15x3 - 5x2 +10x

Gii: 15x3 - 5x2 +10x =

= 5x.3x2 - 5x.x + 5x.2

= 5x.(3x2 x +2)

- Ghi ni dung ?1 ln bng

- Yu cu HS lm bi theo nhm nh, thi gian lm bi l 5

- Yu cau i din nhm trnh by

- Cc nhm nhn xt ln nhau

- GV sa ch sai v lu cch i du hng t c nhn t chung

- Ghi bng ni dung ?2

* Gi : Mun tm x, hy phn tch a thc 3x2 6x thnh nhn t

- Cho c lp nhn xt v cht li - HS lm ?1 theo nhm nh cng bn.

- i din nhm lm trn bng ph. Sau trnh by ln bng

a) x2 x = x.x x.1 = x(x-1)

b) 5x2(x 2y) 15x(x 2y)

= 5x.x(x-2y) 5x.3(x-2y)

= 5x(x-2y)(x-3)

c) 3(x - y) 5x(y - x)

= 3(x - y) + 5x(x - y)

= (x - y)(3 + 5x)

- C lp nhn xt, gp

- HS theo di v ghi nh cch i du hng t

- Ghi vo v bi ?2

- Nghe gi , thc hin php tnh v tr li

- Mt HS trnh by bng

3x2 6x = 0

( 3x . (x 2) = 0

( 3x = 0 hoc x 2 = 0

( x = 0 hoc x = 2

- C lp nhn xt, t sa sai 2/ Ap dng :

Gii?1 :

a) x2 x = x.x x.1 = x(x-1)

b) 5x2(x 2y) 15x(x 2y)

= 5x.x(x-2y) 5x.3(x-2y)

= 5x(x-2y)(x-3)

c) 3(x - y) 5x(y - x)

= 3(x - y) + 5x(x - y)

= (x - y)(3 + 5x)

* Ch : A = - (- A)

Gii ?2 :

3x2 6x = 0

( 3x.(x 2) = 0

( 3x = 0 hoc x 2 = 0

( x = 0 hoc x = 2

4. Cng c:


- Cho HS lm bi 39/19 SGK

( GV chia lp thnh 2, mt na gii cu b, d, mt na gii cu c, e

( GV nhc nh HS cch tm cc s hng vit trong ngoc: ly ln lt cc hng t chia cho nhn t chung.

( GV nhn xt bi lm ca HS

- Cho HS lm bi 40b/19

( tnh nhanh gi tr ca biu thc ta nn lm th no?

- HS lm bi trn bng nhm

kt qu:

b) x2 (+ 5x + y)

c) 7xy(2x 3y + 4xy)

d) (y 1) (x y)

e) 2( x y) (5x + 4y)

( HS nhn xt bi lm ca bn

( Yu cu HS lm vo v, 1 HS ln bng gii - HS nn phn tch a thc thnh nhn t ri mi thay gi tr ca x v y vo tnh

- HS lm vo v, 1 HS ln bng Bi 40b

Ta c:

x(x 1) y(1 x)

= x(x - 1) + y(x 1)

= (x 1) (x + y)

Thay x = 1999 vo biu thc ta c:

(2001 1) (2001 + 1999)

= 2000 . 4000

= 8000000

5. Dn d:Hot ng ca thyHot ng ca trNi dung bi

- c Sgk lm li cc bi tp v xem li cc bi tp lm

- Bi 41 trang 19 Sgk

* Tng t ?2

- Bi 42 trang 19 Sgk

* 55n+1 = ?

- Xem li 7 hng ng thc tit sau hc bi 7- HS nghe dn v ghi ch vo tp

- Ch du, t n kt qu cui cng

- Nhn 2 lu tha cng c s

- Xem li 7 hng ng thc ng nh Bi 41 trang 19 Sgk

Bi 42 trang 19 Sgk


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Ngy son :

Ngy dy:

Lp:

Tit 10

7. PHN TCH A THC THNH NHN T BNG

PHNG PHP DNG HNG NG THC

I. MC TIU1. Kin thc : HS hiu cch phn tch a thc thnh nhn t bng phng php dng hng ng thc.

2. K nng : HS bit vn dng cc hng ng thc hc vo vic phn tch a thc thnh nhn t. Vn dng gii ton.

3. Thi : Rn k nng quan st, linh hot khi lm ton. II. CHUN B:- Thy:+ Bng ph ghi cc bi tp mu

+ kim tra 15pht

- HS: Bng nhm + n bi c.

III. TIN TRNH TIT DY:1. n nh 2. Kim tra: Cho HS kim tra 15 pht .Cu hip n

Cu 1: Vit tip vo v phi c cc hng ng thc :

A2 + 2AB + B2 =

A2 ( 2AB + B2 =

A2 B2 =

A3 + 3A2B + 3AB2 + B3 = A3 ( 3A2B + 3AB2 ( B3 = A3 + B3 =

A3 ( B3 =

Cu 2: Tm x bit :

x3 13x = 0

1. A2 + 2AB + B2 = (A + B)2A2 ( 2AB + B2 = (A ( B)2A2 B2 = (A + B)(A B)A3 + 3A2B + 3AB2 + B3 = (A + B)3

A3 ( 3A2B + 3AB2 ( B3 = (A B)3A3 + B3 = (A + B)(A2 AB + B2)A3 ( B3 = (A ( B)(A2 ( AB + B2)

2. Tm x bit :x3 13x = 0

x(x 13) = 0

x = 0 hoc x 13 = 0

x = 0 hoc x = 13

3. Bi mi:Hot ng ca thyHot ng ca trNi dung bi

Cho HS thc hin phn v d:

GV ghi ln bng 1. V d

Phn tch cc a thc sau thnh nhn t

( Xt v d a): c th dng phng php t nhn t chung phn tch a thc x2 4x + 4 thnh nhn t c khng? V sao

( GV: a thc ny c 3 hng t, em hy ngh xem c th p dng HT no bin i thnh tch?HS: Khng thc hin c v tt c cc hng t ca a thc khng c nhn t chung.

HS: a thc trn c th vit c di dng (A B)2a) x2 4x + 1

b) x2 2

c) 1 8x3gii

a) x2 4x + 4

= x2 2x .2 + 22= (x 2)2b) x2 2 = x2 ()2= (x + ) (x - )

c) 1 8x3 = 1 (2x)3= (1 2x) (1 + 2x + 4x2)

( GV gi HS thc hin

( GV gii thiu cch lm nh trn gi l phn tch a thc thnh nhn t bng phng php HT( HS tr li ming (gv ghi bng)

( GV yu cu HS t nghin cu hai v d b v c trong sch gio khoa trang 19

( Qua phn t nghin cu em hy cho bit mi v d s dng HT no phn tch a thc thnh nhn t?

- GV hng dn HS lm

a) Phn tch a thc

x3 + 3x2 + 3x + 1 thnh nhn t: ( HS t nghin cu SGK, 2HS ln trnh by

( HS tr li:

A2 B2, v d c dng HT: A3 B3

- a thc ny c 4 hng t, bc cao nht ca bin l 3, theo em c th p dng hng ng thc no?HS: C th dng HT (A + B)3

( Gi HS thc hin( Mt HS thc hin

x3 + 3x2 + 3x + 1

= x3 + 3.x2.1 + 3x.12 + 13= (x + 1)3

b) Phn tch a thc

(x + y)2 - 9x2 thnh nhn t

( Gi HS nhn dng biu thc

( Gi HS thc hin

( Gi HS nhn xt( HS: a thc c dng A2 B2( HS thc hin

(x + y)2 9y2= (x + y)2 (3y)2= (x + y + 3x) (x + y 3x)

= (4x + y) (y 2x)

- Yu cu HS thc hin tip

( Gi HS nhn xt

- 1 HS ln bng, c lp lm v nhp

1052 25 = 1052 - 52= (105 5) (105 + 5)

= 100 . 110

= 11000

- Cho HS lm phn p dng

( GV cho HS quan st bi trn bng ph( HS c bi2. p dng

( chng minh a thc chi ht cho 4 vi mi s nguyn n cn lm th no.( HS .bin i a thc thnh dng tch trong c c 1 tha s l bin ca HV d: (SGK trg 26)

gii:

Ta c:

(2n + 5)2 25

= (2n + 5)2 - 52= (2n + 5-)(2n+5+5)

= 2n (2n + 10)= 4n (n + 5)

( y thc t l i phn tch a thc thnh nhn tNn (2n + 5)2 25 chia ht cho 4 vi mi s nguyn n

( Cho HS lm bi vo v, 1 HS ln bng lm- HS lm vo v, 1HS ln bng lm, HS lm bi vo v

( Cho HS nhn xt, GV sa sai (nu c).- HS nhn xt bi lm ca bn

4. Cng c:


Cho HS lm bi tp 43/20 SGK

( Cho mi dy lm 2 bi (a v c, b v d)( HS lm vo v theo quy nh ca GV

( Gi 4 HS ln bng gii( 4 HS ln bng gii

( GV nhn xt, sa sai nu c( HS nhn xt bi gii kt qu:

a) (x + 3)2 b) (x + 5)2c) (2x-)(4x2 + x +)

d) (x 8y)(x + 8y)

5. Dn d:

- n li bi, ch vn dng hng ng thc cho ph hp

- Gii cc bi tp 44, 45, 46/20 SGK + 29, 30/6 SGK

IV. RT KINH NGHIM TIET DY:..........................................................................................................................................................................................................................................................................................................................

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Tun:

Ngy son :

Ngy dy:

Lp:

Tit 11

8. PHN TCH A THC THNH NHN T BNG PHNG PHP NHM HNG T

I. MC TIU:

1. Kin thc :HS bit phn tch a thc thnh nhn t bng phng php nhm hng t .

2. K nng : HS bit nhm cc hng t mt cch thch hp phn tch a thc thnh nhn t, khi nhm cc hng t ng trc du ngoc l du th i du cc hng t trong du ngoc, vn dng phn tch a thc thnh nhn t mt s dng ton .

3. Thi : Rn k nng quan st, linh hot khi gii ton.II. CHUN B:

Thy: Bng ph ghi bi gii mu, bi.

Tr: Bng nhm


1. n nh 2. Kim tra Gi 2 HS ln bng

HS1: Cha bi 44c/20 SGK

(a + b)3 + (a b)3

= (a3 + 3a2b + 3ab2 + b3) + (a3 - 3a2b + 3ab2 - b3)

= 2a3 + 6ab2= 2a(a2 + 3b2)

Hi thm: cn cch gii no khc khng?

HS: Dng hng ng thc A3 + B3GV: Cho hc sinh quan st bi gii theo cch trn (ghi sn bng ph)

(a + b)3 + (a - b)3= [(a + b) + (a b)][(a + b)2 (a + b)(a-b)+(a-b)2]

= (a + b + a b)(a + 2ab + b2a2 +b2 +a2 2ab+b2)

= 2a(a3 + 3b3)

HS2: Gii bi tp 29b/6 SBT

Tnh nhanh:

872 + 732 272 132

= (872 272) + (732 132)

= (87 27) (87 + 27) + (73 13) (73 + 13)

= 60 . 114 + 60 . 86

= 60 (114 + 86)

= 60 . 200

= 12000

GV: cn cch no khc tnh nhanh bi tp trn:

HS: (872 132) + (732 272)

= (87 13) (87 + 13) + (73 27) (73 + 27)

= 74 . 100 + 46 . 100

= (74 + 46) . 100 = 12000

GV: Nhn xt, ghi im

- Qua bi tp ny ta thy phn tch a thc thnh nhn t cn c thm phng php nhm cc hng t.

( GV gii thiu bi mi

3. Bi mi:Hot ng ca thyHot ng ca trNi dung bi

- GV a v d 1 ln bng cho hc sinh thc hin, nu lm c th gio vin khai thc, nu khng lm c th gio vin gi cho hc sinh.HS tr li ming1. V d

( C th vn dng 2 phng php hc gii bi tp ny c khng?( Khng vn dng c v c 4 hng t khng c nhn t chung

( Trong 4 hng t, nhng hn t no c nhn t chung.( x2 v 3x; xy v 3y hoc x2 v xy; -3x v 3yV d1: Phn tch a thc sau thnh nhn t:

X2 3x + xy 3y

( Hy nhm cc hng t c nhn t chung v t nhn t chung cho tng nhm( x2 3x + xy - 3y

= (x2 3x) + (xy 3y)

= x(x 3) + y(x 3)Gii

( n y cc em c nhn xt g?( Gia 2 nhm li c nhn t chung l x 3x2 3x + xy 3y

= (x2 3x) + (xy 3y)

= x(x 3) + y (x 3)

= (x 3) (x + y)

Cch khc:

x2 3x + xy 3y

= (x2 + xy) + (-3x 3y)

= x(x + y) 3( x + y)

= (x y) (x 3)

( Hy t nhn t chung ca cc nhm( HS thc hin

( Em c th nhm hng t theo cch khc c khng?

( GV lu khi HS nhm cc hng t m t du - trc ngoc th phi i du tt c cc hng t trong ngoc

( GV gii thiu hai cch lm nh v d trn gi l phn tch a thc thnh nhn t gi l phng php nhm hng t. ( HS thc hin

- GV a v d 2: yu cu HS bng cc cch nhm khc nhau. Hy phn tch a thc thnh nhn t.- HS c lp cng thc hin

- 2 HS ln bng trnh byV d 2: Phn tch a thc sau thnh nhn t:

2xy + 3z + 6y + xz

gii

cch 1:

2xy + 3z + 6y + xz

= (2xy + 6y) + (3z = xz)

= 2y (x + 3) + z (3 + x)

= (x + 3) (2y + z)

Cch 2:

- GV hi: C th nhm (2xy + 3z) + (6y + xz) c khng? Ti sao?( HS: Khng. Vi nhm nh vy khng

phn tch c a thc thnh nhn t2xy + 3z + 6 + xz

= (2xy + xz) + (3z + 6y)

= x(2y + z) + 3 (z + 2y)

= (2y + z) (x + 3)

- GV: Vy khi phn tch a thc thnh nhn t bng phng php nhm hng t phi nhm thch hp, c th l:

+ Mic nhm u c th phn tch c.

+ Sau khi phn tch a thc thnh nhn t mi nhm th qu trnh phn tch phi tip thu c.

- GV lu : i vi mt a thc c nhiu cch nhm hng t. Cch lm nh cc v d trn gi l phn tch a thc thnh nhn t bng phng php nhm hng t.

** Ch : i vi mt a thc c th c nhiu cch nhm nhng hng t thch hp.

- GV cho HS lm 2. p dng:

( Cho HS lm vo v

( 1 HS ln bng trnh by- HS lm bi vo v, 1 HS ln bng thc hinTnh nhanh:

- GV cho HS quan st bi trn bng ph

( Gi HS nu kin ca mnh v li gii ca cc bn

( Gi 2 HS ln bng phn tch tip vi cch lm ca bn Thi v bn H.- HS: Bn An lm ng, bn Thi v bn H cha phn tch ht v cn c th phn tch tip c.

- 2 HS ln bng phn tch tip bi ca 2 bn Thi v H 15 .64 + 25 . 100 + 36 .15 + 60 .100

= 15(64 + 36) + 100 (25 + 60)

= 15 .100 + 100. 85

= 1500 + 8500

= 10000

4. Cng c:


- Yu cu HS hot ng nhm, na lp lm bi 48b, na lp lm bi 48c/22 SGK

- GV lu HS

( Nu tt c cc hng t ca a thc c tha s chung th nn t tha s trc ri mi nhm

( Khi nhm, ch ti cc hng t hp thnh hng ng thc - HS hot ng theo nhm.

48b) 3x2 + 6xy + 3y2 3z2= 3(x2 + 2xy + y2 z2)

= 3 [(x + y)2 z2]

= 3 (x + y + z) (x + y z)

48c)

x2 2xy + y2 z2 + 2zt - t2)

=.

= (x y + z t) (x y z + t)

( i din cc nhm trnh by bi gii.

- GV kim tra bi lm mt s nhm.( HS nhn xt

- Cho HS nhn xt bi gii trn bng, gio vin nhn xt chung v sa sai (nu c).

5. Dn d:- Khi phn tch a thc thnh nhn t bng phng php nhm hng t cn nhm thch hp.

- n tp 3 phng php phn tch a thc thnh nhn t hc.

- Gii cc bi tp 47, 48a, 49, 50/22 SGK

- Gii cc bi tp 31, 32, 33/6 SBT


.......................................................................................................................................................................................................................................................................................................................... .......................................................................................................................................................................................................................................................................................................................... ............................................................................................................................................................. Tun:

Ngy son :

Ngy dy:

Lp:

Tit 12

LUYEN TAPI. MUC TIEU:

- KT: Ren luyen k nang giai bai tap phan tch a thc thanh nhan t bang cac phng phap:at tha so chung, dung hang ang thc ang nh, nhom cac hang t.

- KN: HS giai thanh thao loai bai tap nay, ong thi biet van dung mot cach linh hoat cac phng phap phan tch mot cach hp ly va nhanh chong.

- T: Gio dc tnh cn thn v chnh xc.

II. CHUAN B:

Phieu hoc tap, bang phu.

III. TIEN TRNH TIET DAY :

1).On nh :

2).Kiem tra : Kim tra trong lc luyn tp.

3).T chc luyn tp

Hoat ong cua ThyHoat ong cua TroNoi dung ghi

Giao vien cho hoc sinh trnh bay bai tap 48c/22 SGK.

GV:trong a thc nay co may hang t, e phan tch nhanh chung ta can ap dung phng phap nao?

Giao vien cho hoc sinh trnh bay bai tap 49b/22 SGK.

GV:Phai nhom nh the nao e tnh nhanh nhat?

Giao vien cho hoc sinh trnh bay bai tap 50/23 SGK.

GV: e tm x cac em bien oi ve trai nh the nao?

GV: Cho hoc sinh lam bai tap dang toan chia het o la bai 52/23 SGK.

GV: Hay bien oi a thc thanh mot tch?

Hoc sinh len bang trnh bay BT 48c/22 SGK.

HS: thc hien bai tap49b/22 SGK

HS t lam tren nhap va tra li ket qua bangnhom.

HS:Bien oi ve trai thanh mot tch va van dung kien thc A.B=0 khi A=0 hoac B = 0.

HS: Lam BT 52/24 SGK

HS: Bien oi a thc thanh mot tch trong o co mot tha so chia het cho 5.

HS: Len bang trnh bay bai lam.

BT 48/22 SGK:

c)x2-2xy+y2-z2+2zt-t2=( x2-2xy+y2)-( z2-2zt+t2)

=(x-y)2-(z-t)2=(x-y-z+t)( x-y+z-t).

BT49b/22 SGK:

Tnh nhanh

452+402-152+80.45

=(452+80.45+402)-152=(45+40)2-152=852-152 =70.100=7000.

BT50/23 SGK

b) 5x(x-3)-x+3 = 0

5x(x-3)-(x-3) = 0

(x-3)(5x-1) = 0

x-3 = 0 hoac5x-1=0

x = 3; x =.

BT52/24SGK:

C/M: (5n+2)2-4 chia het cho 5, nZ

Ta co:

(5n+2)2+4 =(5n+2+2)(5n+2-2)

=5n(5n+4) luon chia het cho5 nZ

4. Cng c:

Cho HS nhc li cc phng php lm i vi cc bi tp trn.

5). Dn d:

Bai tap:Phan tch cac a thc sau thanh nhan t

a) x2-2xy+y2-9

b) x2-3x+2IV. RT KINH NGHIM TIT DY

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..........................................................................................................................................................Tun:

Ngy son :

Ngy dy:

Lp:

Tit 13

9. PHN TCH A THC THNH NHN TBNG CCH PHI HP NHIU PHNG PHP

I. MC TIU: Kin thc : HS bit phn tch a thc thnh nhn t bng cch phi hp nhiu phng php.K nng : HS bit vn dng mt cch linh hot cc phng php phn tch a thc thnh nhn t hc vo vic gii ton phn tch a thc thnh nhn t.

Thi : Rn k nng quan st, tnh cn thn khi lm ton.II. CHUN B:

Thy: Bng ph ghi bi tp tr chi Thi Gii ton nhanh

Tr: Bng nhm

III. TIN TRNH TIT DY: 1. n nh 2. Kim tra: Gi 2 HS ln bng

HS1 gii bi 50b SGK

Tm x:

5x (x 3) x + 3 = 0

5x ( x - 3) ( x 3) = 0

( x- 3)(5x 1) = 0

=> x 3 = 0; 5x 1 = 0

=> x = 3; x =

HS2: Gii bi 32b/6 SBT (yu cu nhm theo 2 cch)

Phn tch a thc thnh nhn t:

C1: a3 a2x ay + xy

= (a3 a2x) (ay xy)

= a2 (a x) y(a x)

= (a x) (a2 y)

C2: a3 a2x ay + xy

= (a3 ay) (a2x xy)

= a2 (a2 y) x(a2 y)

= (a2 y) (a x)

GV nhn xt, ghi im

3. Bi mi:Gii thiu bi: Hi: Hy nhc li cc phng php phn tch a thc thnh nhn t hc?

GV: Trn thc t ta thng phi hp nhiu phng php ( gii thiu bi mi.


- GV cho HS theo di v d 11. V d

( Vi bi ton trn em c th dng phng php no phn tch?- HS: t nhn t chung l 5x V d 1: Phn tch a thc sau thnh nhn t:

5x3 + 10x2y + 5xy2

( n y loi bi ton dng li cha? V sao?- HS: Cn phn tch tip c v trong ngoc l biu thc c dng (A + B)2gii:

5x3 + 10x2y + 5xy2= 5x (x2 + 2xy + y2)

= 5x (x + y)2

( Nh vy phn tch a thc 5x3 + 10x2y + 5xy2 thnh nhn t u tin ta dng phng php t nhn t u tin ta dng phng php t nhn t chung sau dng tip phng php dng HT

- GV cho HS quan st v d 2.HS:V d 2: Phn tch a thc sau thnh nhn t:

( v d ny, em c dng phng php t nhn t chung khng? Ti sao?- Khng, v c 4 hng t ca a thc khng c nhn t chung.x2 2xy + y2 9

gii

( Em nh dng phng php no? c th? HS: . Nhm cc hng t ri dng HT x2 2xy + y2 9

= (x2 2xy + y2) 9

= (x y)2 - 32= (x y+3)(xy 3)

( GV cho HS quan st trn bng ph cc cch nhm:

x2 2xy + y2 9

= (x2 2xy) + (y2 9)

Hoc

- (x2 2xy) + (y2 2xy) HS: Khng c v:

(x2 2xy) + (y2 9)

= x (x 2y) + (y 3) (y + 3)

th khng phn tch tip c

Hoc

=(x2 9) + (y2 2xy)

= (x 3) (x + 3) + y(y 2x) cng khng phn tch tip c

( GV nu mt s bc quan trng trong khi phn tch a thc thnh nhn t.

- t nhn t chung nu cc hng t u c nhn t chung.

- Dng HT nu c

- Nhm nhiu hng t (thng mi nhm c nhn t chung hoc l dng HT) nu cn thit phi t du - trc ngoc v i du cc hng t.

- Yu cu HS lm - HS lm bi vo v

- 1 HS ln bng lm

2x3y 2xy34xy2 2xy

= 2xy(x2y2 2y 1)

= 2xy[x2(y2 +2y + 1)]

= 2xy [x2 (y + 1)2]

= 2xy(xy1)(x+y+ 1)

-Cho HS thc hin theo nhm phn a

( GV cho cc nhm kim tra kt qu lm ca nhm mnh.

.GV cho HS cu b) trn bng ph. Yu cu HS ch r cch lm ca bn Vit dng nhng phng php no phn tch a thc thnh nhn t.

- HS hot ng nhm phn a

( Phn tch x2 + 2x + 1 y2 thnh nhn t:

..= (x + 1 + y) ( x + 1 y)

( Thay x = 94,5; y = 4,5 vo a thc sau khi phn tch ta c:

----= 9100

( i din nhm trnh by)

- HS . Cc phng php nhm hng t, dng hng ng thc 2) p dng:

Tnh nhanh gi tr ca biu thc:

x2 + 2x + 1 y2

ti x = 94,5; y = 4,5

Gii:

Ta c: x2 + 2x + 1 y2 = ...

=(x + 1 + y) ( x + 1 y). Thay x = 94,5; y=4,5 ta c:

= ...

= 9100

4. Cng c:


Cng c:

GV t chc cho HS thi lm ton nhanh.

: phn tch a thc thnh nhn t v nu cc phng php m i mnh dng

i 1: 20z25x210xy 5y2i 2: 2x 2yx2+2xy y2Yu cu: Mi i gm 5 HS. Mi HS ch c vit 1 dng (trong qu trnh phn tch a thc thnh nhn t) HS cui cng vit cc phng php m i mnh dng khi phn tch. HS sau c quyn sa sai ca HS trc. i no lm nhanh v ng l thng.Kt qu:

i 1: 20z25x210xy 5y2= 5(4z2 x22xy y2)

= 5[(2z)2 (x + y)2]

= 5(2zxy)(2z+x+ y)

Phng php: t nhn t chung nhm hng t, dng HT

i 2:

2x 2y x2 + 2xy y2=(2x2y)(x22xy+ y2)

= 2 (x y) ( x y)2= ( x y) [2 (x y)]

= ( x y) (2 x + y)

- Sau cng GV cho HS nhn xt, cng b i thng cucPhng php: nhm hng t, dng HT, t nhn t chung.

5. Dn d:- n li cc phng php phn tch a thc thnh nhn t

- Gii cc bi tp 52, 54, 55/25 SGK + 34/7 SBT

- Nghin cu phng php tch hng t phn tch a thc thnh nhn t qua bi tp 53/24 SGK.


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Tun:

Ngy son :

Ngy dy:

Lp:

Tit 14

LUYN TP (9)

I.MC TIU:- KT: Rn luyn k nng gii bi tp phn tch a thc thnh nhn t.

- KN: HS gii thnh tho loi bi tp phn tch a thc thnh nhn t .

- T: Cng c, khc su, nng cao k nng phn tch a thc thnh nhn t.

II.CHUN B:Thy: Bng ph ghi sn bi tp 53a

Tr: Bng nhmIII. TIN TRNH TIT DY:1. n nh 2. Kim tra: gi 2 HS ln bng

HS1: Gii bi tp 51 a, (SGK)

Phn tch a thc thnh nhn t:

a) x3 2x2 + x = x(x2 2x + 1) = x (x 1)2b) 2x2 + 4x + 2 2y2 = 2 (x2 + 2x + 1 y2) = 2 [(x2 + 2x + 1) y2) =.

= 2 (x + 1 + y) (x + 1 y)

HS2: Gii bi tp (SGK)

Chng minh rng (5n + 2)2 4 chia ht cho 5 vi mi s nguyn n.

Ta c: (5n + 2)2 4 = (5n + 2)2 - 22 = (5n + 2 2) (5n + 2 + 2) = 5n (5n + 4)

Vy... lun chia ht cho 5 vi mi n(Z

- GV nhn xt cho im

- Hi: Khi phn tch a thc thnh nhn t ta tin hnh nh th no?

(p:

- t nhn t chung nu tt c cc hng t c nhn t chung .

- Dng hng ng thc (nu c)

- Nhm nhiu hng t (thng mi nhm c nhn t chung hoc l hng ng thc); cn thit phi t du - trc du ngoc v i du hng t trong ngoc.

3. T chc luyn tp:Gii thiu bi: Trong tit ny chng ta s lm mt s bi tp cc em nm vng pp phan tch a thc thnh nhn t.Hot ng ca thyHot ng ca trNi dung bi

+ Cho HS lm bi tp 54/251. Bi tp 54/25 (SGK)

- Gi 3 HS ln bng (mi HS lm 1 phn)+ 3 HS ln bng thc hin theo yu cu GV a)x3 + 2x2y + xy2 9x

= x (x2 + 2xy + y2 9)

=..

= x(x + y +3)(x + y 3)

b) 2x 2y x2+2xy y2= 2 (x y) (x y)2= (x y) (2 x + y)

- Yu cu HS nhn xt sa sai (nu c)- HS nhn xt ..c) x4 2x2 = x2 (x2 2)

= x2 (x + ) (x - )

+ Cho HS lm bi 55(a, b) trang 25/SGK 2. Bi tp 55/25 (SGK)

a) x3 - x = 0

- GV yu cu HS suy ngh v hix (x2 - ) = 0

- tm x trong bi ton trn em lm th no?HS: phn tch a thc v tri thnh

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