已知2x-y=10,求[(x²+y²)-(x-y)²+2y(x-y)]/4y的值

问题描述:

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

[(x²+y²)-(x-y)²+2y(x-y)]/4y=(x²+y²-x²+2xy-y²+2xy-2y²)/4y =(4xy-2y²)/4y =[2y...