这题错了吧x(x+y)(x-y)-x(x+y)^2x(x+y)(x-y)-x(x+y)^2=x(x+y)[(x-y)-(x+y)]=x(x+y)(-2y)=-2xy(x+y)=-2*(1/2)*1=-1不明白可追问，满意请采纳为什么可以这样写：=x(x+y)[(x-y)-(x+y)]数学不好别说我笨提取公因式x(x+y)谢谢，终于弄懂了不客气