问题 解答题

将下列各式因式分

(1)9m2-4n2

(2)x3-9x

(3)-3ma2+12ma-9m

(4)n2(m-2)+4(2-m)

(5)(x-3)(x-7)+4

(6)2(x+y)(x-y)-(x+y)2-(x-y)2

(7)a2-b2-a+b.

答案

(1)原式=(3m+2n)(3m-2n);

(2)原式=x(x2-9)=x(x+3)(x-3);

(3)原式=-3m(a2-4a+3)=-3m(a-1)(a-3);

(4)原式=n2(m-2)-4(m-2)=(m-2)(n2-4)=(m-2)(n+2)(n-2);

(5)原式=x2-10x+21+4=x2-10x+25=(x-5)2

(6)原式=-[(x+y)2-2(x+y)(x-y)+(x-y)2]=-[(x+y)-(x-y)]2=-(2y)2=-4y2

(7)原式=(a+b)(a-b)-(a-b)=(a-b)(a+b-1).

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