化简：
(m-2n)^2 (m+2n)^2（m^2+4n^2）^2
=[(m-2n) (m+2n)]^2（m^2+4n^2）^2
=（m^2-4n^2）^2（m^2+4n^2）^2
=[（m^2-4n^2）（m^2+4n^2）]^2
=(m^4-16n^4)^2