你题目打错了吧，(x+y)²-(x+y)²=0啊是否应为(x+y)²-(x-y)²=((x+y)+(x-y))((x+y)-(x-y))=(2x)(2y)=4xy
(x+y)的二次方-(x-y)的二次=【x＋y＋x-y】【x＋y-x+y】=4xy
(x+y)²-(x-y)²=（x+y+x-y）(x+y-x+y)=(2x)(2y)=4xy祝你学习进步！
?(x+y)的二次看不懂
