（x+y)×(x-y)+(x-y)的平方-（x平方-3xy)等于多少,大哥大姐帮帮忙啊

题目

（x+y)×(x-y)+(x-y)的平方-（x平方-3xy)等于多少,大哥大姐帮帮忙啊

答案

(x+y)(x-y)+(x-y)²-(x²-3xy)
=(x-y)[(x+y)+(x-y)]-x(x-3y)
=2x(x-y)-x(x-3y)
=x[2(x-y)-(x-3y)]
=x(x+y)