已知2x-y=10,求[(x²+y²)-(x-y)²+2y(x-y)]/4y的值
我是这样做的,老师说不对：[(x²+y²)-(x-y)²+2y(x-y)]/4y=（x²+y²-x²+2xy-y²+2xy-2y²）/4y=（4xy-2y²）/4y=[2y（2x-y）]/4y=二分之一（2x-y)=二分之一乘10=5