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).