m^2-2mn+n^2=（m-n）^2
2a^3+8a^2b+8ab^2=2a(a^2+4ab+4b^2)
=2a*(a+2b)^2
a^2(x-y)+b^2(y-x)=(x-y)*(a^2-b^2)
=(x-y)*(a-b)*(a+b)