(a+b)^4-(a+b)^2x^2(x-y)+y^2(x-y)(7m+3n)^2-(5m+7n)^2

问题描述:

(a+b)^4-(a+b)^2
x^2(x-y)+y^2(x-y)
(7m+3n)^2-(5m+7n)^2