x+y分之x²-y²-2X-y分之4x（x-y）+y²
=（x+y）（x-y）/(x+y)-(4x²-4xy+y²)/(2x-y)
=x-y-(2x-y)²/(2x-y)
=x-y-2x+y
=-x
如追加其它问题,采纳本题后点击想我求助,