x^2(x-y)+y^2(y-x)
=x^2(x-y)-y^2(x-y)
=(x-y)(x^2-y^2)
=(x-y)(x-y)(x+y)
=(x-y)^2(x+y)（x-y)(x-y)2(y-x)中的2平方，？是二分之一急用！谢谢