（3a/x+y）的三次方乘以（x二次方-y二次方）除以（y-x/y+x）二次方
问题描述：
（3a/x+y）的三次方乘以（x二次方-y二次方）除以（y-x/y+x）二次方
答
(3a/x+y)³*(x²-y²)/(y-x/y+x)²
=(3a)³/(x+y)³*(x+y)*(x-y)*(x+y)²/(x-y)²
=(3a)³/(x-y)