9（m-n)(m+n)-3(m-n)平方
=3(m-n)(3m+3n-m+n)
=3(m-n)(2m+4n)
=6(m-n)(m+2n)
.
3（x+y)(y-x)-(x-y)平方
=3（x+y)(y-x)-(y-x)平方
=(y-x)(3x+3y-y+x)
=(y-x)(4x+2y)
=2(y-x)(2x+y)
.
3m(x-y)(a-b+c)+6n(y-x)(b-a-c)
=3m(x-y)(a-b+c)+6n(x-y)(a-b+c)
=3(x-y)(a-b+c)(m+2n)