4（m+2n）²-9（2n-m）²
=[2(m+2n)-3(2n-m)][2(m+2n)+3(2n-m)]
=(2m+4n-6n+3m)(2m+4n+6n-3m)
=(5m-2n)(10n-m)
a²-b²=(a-b)(a+b)