x三次方y三次方(x-y)三次方+x平方y平方(y-x)平方
=x三次方y三次方(x-y)三次方+x平方y平方(x-y)平方
=x²y²(x-y)²[xy(x-y)+1]
=x²y²(x-y)²(x²y-xy²+1)