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# 15.2 平方差公式(参赛课件)--

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m2 - 4 (2) (m+2)(m-2) =
(3) (2x+1)(2x-1) = 4x2 - 1

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(a+b)(a-b) =

2-b2 a

(a+b)(a-b) 2-ab+ab-b2 = a -ab+ab 2-b2 =a b
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§15.2.1

2-b2 (a+b)(a-b)=a

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a a-b a

a

b

(a+b)(a-b)

b

b

a-b

(a+b)(a-b)=a2-b2
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2-b2 (a+b)(a-b)=a

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2-b2 (a+b)(a-b)=a

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2-b2 (a+b)(a-b)=a

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2-b2 (a+b)(a-b)=a

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1.下列各式中,能用平方差公式运算的是( A ) A.(-a+b)(-a-b) B.(a-b)(b-a)

C.(2a-3b)(3a+2b)

D.(a-b+c)(b-a-c)

2.下列多项式相乘,不能用平方差公式计算的是(C) A.(x-2y)(2y+x) C.(-2y-x)(x+2y) B.(-x+2y)(-x-2y) D.(-2b-5)(2b-5)

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⑴ (3x+2)(3x-2) ; ⑵ (b+2a)(2a-b); (3) (-x+2y)(-x-2y).

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⑴ (3x+2)(3x-2) = (3x)2 - 22 3x 2 3x 2

( a +b) (a - b) = a2 - b2

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(1) (x+2)(x-2) = x2 - 2 (2) (-3a-2)(3a-2) = 9a2 X2 - 4 4 4 - 9a2

ㄨ ㄨ

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(2) (3+2a)(-3+2a) = 4a2 - 9

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98 ⑴ 102 ×98 = (100+2) (100-2) = 1002-22 = 10000-4 = 9996
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y 2 y2 y1 y 5 ⑵ (y+2)(y-2)-(y-1)(y+5)

= y2 - 22 - (y2+4y-5)
= y2-4-y2-4y+5 = -4y+1
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1、(m+n)(-n+m) =
2、(-x-y) (x-y) =

m2-n2 y2-x2 4a2-b2 x4-y4

3、(2a+b)(2a-b) = 4、(x2+y2)(x2-y2)=

5、 51 × 49

=

2499
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1、(3x+4)(3x-4) – (2x+3)(3x-2); 2、(x+y)(x-y)(x2+y2);

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(2+1)(22+1)(24+1)(28+1) … (22n+1)

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