当x+y/x-y=1/2时,求代数式x-y/x+y-2x+2y/x-y的值
问题描述：
当x+y/x-y=1/2时,求代数式x-y/x+y-2x+2y/x-y的值
答
x+y/x-y=1/2
取倒数
x-y/x+y=2
所以
x-y/x+y-2x+2y/x-y
=x-y/x+y-2(x+y/x-y)
=2-2×1/2
=2-1
=1