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TiTit 46: LUYt 46: LUYN TN TPP(( V V phép cphép cng các sng các s nguyên)nguyên)

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KiÓm tra bµi cñ

Ph¸t biÓu quy t¾c céng hai sè nguyªn©m?Muèn céng hai sè nguyªn ©m ,ta céng

hai gi¸ trÞ tuyÖt ®èi cña chóng råi®Æt dÊu ³-´ tr-íc kÕt qu¶ .

¸p dông tÝnh: a/ (-17) +(- 43) =- 60b/ (-28) +(- 43) =-71

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¸p dông tÝnh: (+17) +(- 43)= - ( 43 - 17 )

= 26

Ph¸t biÓu quy t¾c céng hai sè nguyªn kh¸cdÊu?

Muèn céng hai sè nguyªn kh¸c dÊukh«ng ®èi nhau ,ta t×m hiÖu hai gi¸trÞ tuyÖt ®èi cña chóng(sè lín trõ sè

nhá)råi ®Æt tr-íc kÕt qu¶ t×m ®-îcdÊu cña sè cã gi¸ trÞ tuyÖt ®èi lính¬n .

8/3/2019 Tiet 46 Luyen Tap Ve Phep Cong 2 So Nguyen

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TiÕt 47 Luy n t pD¹ng 1: TÝnh gi¸ trÞ biÓu thøc,so s¸nh

hai sè nguyªn .Bµi 1: TÝnh

a) (-50) + (-10) =- (50+10)

= -60b) 43 + (-3) = 43 - 3 = 40

c)207 + (- 207) =207- 207 = 0d)207 + (- 317) =- (317 ± 207)= - 110

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Bµi 2: TÝnh gi¸ trÞ biÓu thøc :

a) x+ (- 16) biÕt x= - 4Ta thay gi¸ trÞ cña ch÷ vµo biÓu thøc råitÝnhx+ (-16) =(- 4) + (-16) =- 20

-100b) (-102) + y biÕt y = 2

(-102) + y =(-102) + 2 =

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Bµi 3:So s¸nh , rót ra nhËn xÐt :a) 123 + (-)vµ 123123 + (-3) = 120123 + (-3) < 123

b) (-55)+ (-15) vµ (-55)(-55) + (-15) = -70 (-55) + (-15) < (-

55)

NhËn xÐt: Khi céng víi mét sè nguyªn©m ,kÕt qu¶ nhá h¬n sè ban ®Çu .

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c) (-97) + 7 vµ (-97)

(-97) + 7 = ( -90 ) (-97) + 7 > (-97)

NhËn xÐt: Khi céng víi mét sè nguyªnd-¬ng ,kÕt qu¶ lín h¬n sè ban ®Çu .

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D¹ng 2: T×m sè nguyªn x (bµi to¸nng-îc)Bµi 4: Dù ®o¸n gi¸ trÞ cña x vµ kiÓm tra

l¹i : a) x+ (-3) = - 11x= 8 ; (- 8) + (-3) = -11

b) ±5 + x = 15x= 20 ; -5 + 20 = 15

c) + x = -103

x= -13; 3 + (-13 )= -10

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Bµi 5: Thay dÊu * b»ng ch÷ thÝch hîp

a) (- *6 ) + (-24) = -100

(-76) + (-24) = -

100b) 39 + (-1 * ) = 24

39 + (-15) = 24

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D¹ng 3: ViÕt d·y sè theo quy luËt

Bµi 6: ViÕt hai sè tiÕp theo cña mçi d·ysè : a) ± 4 ; -1 ; 2; .....Ta thÊy sè sau lín h¬n sè tr-íc 3 ®¬n

vÞVËy ±4; -1 ; 2 ; 5 ; 8 ; ........

b) 5 ; 1 -3

Ta thÊy sè sau nhá h¬n sè tr-íc 4®¬n vÞVËy 5 ; 1 ; -3 ; -7 ; -11; ........

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Bµi t p n©ng cao :Bµi 1: TÝnh :

a) + a nÕu a 0a u

uNÕu a 0 th× = a khi ®ã +a =a +a = 2a

a a

b) + a nÕu a < 0a

NÕu a < 0 th× =- a khi ®ã +a =-a+a = 2a

a a

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Bµi 2:Chøng minh r»ng sè ®èi cña a ±b lµ b ± a ( a,b Z )

- NÕu tæng (a-b)+( b-a) ta cã:(a-b) +(b-a) = a - b +b - a= (a - a ) +( - b + b )

? A ? Abbaa =

= 0VËy tæng (a-b) vµ (b-a) b»ng 0 nªn a-b vµ b-a ®èi nhau hay a- b = - (b-a)

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H-íng dÉn vÒ nhµ¤n tËp quy t¾c céng hai sè nguyªn ,quy t¾c tÝnh gi¸ trÞ tuyÖt ®èi cña métsè , c¸c tÝnh chÊt phÐp céng sè tù

nhiªn.Lµm bµi tËp 51;52;54;56 trang 60 SBT 

Chµo th©n ¸i