方法一：
4*(m+n)^2-9*(m-n)^2
=(2m+2n)^2-(3m-3n)^2
=(2m+2n+3m-3n)(2m+2n-3m+3n)
=(5m-3)(5n-m)
方法二：
4*(m+n)^2-9*(m-n)^2
=4(m^2+2mn+n^2)-9(m^2-2mn+n^2)
=4m^2+8mn+4n^2-9m^2+18mn-9n^2
=-5m^2+26mn-5n^2
=(5m-3n)(5n-m)