化简x-y/2xy-x²-y²
问题描述：
化简x-y/2xy-x²-y²
答
-（x-y)/（x-y）^2=-1/(x-y)=1/(y-x)
答
(x-y)/(2xy-x²-y²)
=(x-y)/-(x-y)²
=1/-(x-y)
=1/(y-x)