第124页练习第1题答案
解:(1)x-xy2
=x(1-y2)
=x(1+y)(1-y)
(2)9x3-18x2+9x
=9x(x2-2x+1)
=9x(x-1)2
(3)4x2 -1/25
=(2x+1/2)(2x-1/5);
(4)4a-4a2 -1
=-(4ax - 4a+1)
=- (2a-1) 2
第124页练习第2题答案
解:(1)25a2 -4(b+c) 2
=[5a+2(b+c)][5a-2(b+c)1
=(5a+2b+2c)(5a-2b-2c)
(2)(x+y)2+6(x+y)+9
=(x+y) 2+6(x+y)+3 2
=(x+y+3) 2