解
(m-n)(3m+n)²+(m+3n)²(n-m)
=(m-n)(3m+n)²-(m+3n)²(m-n)
=(m-n)[(3m+n)²-(m+3n)²]
=(m-n)[(3m+n)+(m+3n)][(3m+n)-(m+3n)]
=(m-n)(4m+4n)(2m-2n)
=8(m-n)(m+n)(m-n)
=8(m-n)²(m+n)