(m-2n)的平方+(n+2m)的平方
问题描述：
(m-2n)的平方+(n+2m)的平方
答
(m-2n)的平方+(n+2m)
=m^2+4n^2-4mn+n^2+4m^2+4mn
=5m^2+5n^2
答
=[(m-2n)+(n+2m)][(m-2n)-(n+2m)]
=(m-2n+n+2m)(m-2n-n-2m)
=(3m-n)(-m-3n)
=-(3m-n)(m+3n)