16(2m+n)^2-9(m-2n)^2
=[4(2m+n)]^2-[3(m-2n)]^2
=(8m+4n)^2-(3m-6n)^2
=[(8m+4n)+(3m-6n)]*[(8m+4n)-(3m-6n)]
=(11m-2n)(5m+10n)
=5(11m-2n)(m+2n)