因式分解m(x+y)²-4m(x-y)²

题目

因式分解m(x+y)²-4m(x-y)²
..我纠结了3个小时了@@上学就得交了啊
只剩7个小时了啦QAQ

答案

m(x+y)²-4m(x-y)²
=m[(x+y)²-4(x-y)²]
=m[(x+y)²-2²(x-y)²]
=m[(x+y-2(x-y))(x+y+2(x-y))]
=m[(-x+3y)(3x-y)]
=m(3y-x)(3x-y)