最简公分母是xy(x-y)
∴2x+2y/x-y=xy(2x+2y)/xy(x-y)
(x+y)²/xy=(x+y)²(x-y)/xy(x-y)那么x-y/2x+2y与xy/（x+y）²呢？最简公分母是2(x+y)²x-y/2x+2y=(x-y)(x+y)/2(x+y)²xy/（x+y）²=2xy/2(x+y)²