因式分解 公式法 平方差公式

（a+b）²-4b²
=(a+b+2*b)*(a+b-2*b)=(a+3b)(a-b)
（5）9x²-16（a+b）²
=[3x+4(a+b)]*[3x-4(a+b)]
=(3x+4a+4b)(3x-4a-4b)
6）（x+y）³（x-y）-（x+y）（x-y）³
=(x+y)(x-y)[(x+y)^2-(x-y)^2]
=(x+y)(x-y)(x+y+x-y)(x+y-x+y)
=(x+y)(x-y)*2x*2y
=4(x+y)(x-y)xy
（7）25（x-2y）³+4（2y-x）
=(x-2y){[5(x-2y)]^2-2^2}
=(x-2y)*[5(x-2y)+2][5(x-2y)-2]
=(x-2y)*(5x-10y+2)(5x-10y-2)
（8）81a的五次方 b的五次方 -ab
=81a^5*b^5-ab
=ab[(9a^2*b^2)^2-1]
=ab(9a^2*b^2+1)(9a^2*b^2-1)
=ab(9a^2*b^2+1)(3ab+1)(3ab-1)