9（2a+b）^2-16（a-2b）^2
=[3(2a+b)]²－[4(a-2b)]²
=(6a＋3b＋4a－8b)(6a＋3b－4a＋8b)
=(10a－5b)(2a＋11b)
=5(2a－b)(2a＋11b)