因式分解（平方差公式）要过程

a^3-ab^2
=a(a²-b²)
=a(a+b)(a-b)
m^2(x-y)+n^2(y-x)
=(x-y)(m²-n²)
=(x-y)(m+n)(m-n)
2-2m^4
=2(1-m^4)
=2(1+m²)(1-m²)
=2(1+m²)(1+m)(1-m)
3(x+y)^2-27
=3[(x+y)²-9)
=3(x+y+3)(x+y-3)
a^2(b-1)+b^2-b^3
=a²(b-1)-b²(b-1)
=(b-1)(a²-b²)
=(b-1)(a+B)(a-b)
(3m^2-n^2)^2-(m^2-3n^2)^2
=(3m²-n²+m²-3n²)(3m²-n²-m²+3n²）
=(4m²-4n²)(2m²+2n²)
=8(m+n)(m-n)(m²+n²)