楼主看一下是不是打错符号了?(m - n)² - 2(m - n)(x - y)＋(x - y)²=[(m - n) - (x - y)]²=(m - n - x＋y)²(m - n)² - 2(m-n)(x＋y)＋(x＋y)²=[(m-n)-(x＋y)]²=(m-n-x-y)²...