因式分解:(1)(x+y)^2-4 (2) -4a^2+24a-36

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因式分解:(1)(x+y)^2-4 (2) -4a^2+24a-36
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因式分解:(1)(x+y)^2-4 (2) -4a^2+24a-36
因式分解:(1)(x+y)^2-4 (2) -4a^2+24a-36

因式分解:(1)(x+y)^2-4 (2) -4a^2+24a-36
(1)=(x+y)^2-2^2=(x+y+2)(x+y-2)
(2)=-4(a^2-6a+9)=-4(a-3)^2

(1)(x+y+2)*(x+y-2);
(2)-4(a-3)^2=-4*(a-3)*(a-3).

(1)原式=(x+y+2)(x+y-2)
(2)原式=-(4a^2-24a+36)
=-(2a-6)^2

(1)(x+y)^2-4=[(x+y)+2][(x+y-2)]=(x+y+2)(x+y-2)(把x+y)看成一个整体,用平方差的逆运算) (2) -4a^2+24a-36=-(4a^2-24a+36)=-4(a^2-6a+9)=-4(a-3)^2(这道题用了提公因式法和完全平方差公式的逆运算)