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
