4（m+n）²-16（m-n）²=[2（m+n)]²-[4(m-n)]²=[2(m+n)+4(m-n)][2(m+n)-4(m-n)]=(2m+2n+4m-4n)(2m+2n-4m+4n)=(6m-2n)(6n-2m)=2(3m-n)×2(3n-m)=4(3m-n)(3n-m)