9（3a-2b）²-4（a+3b）²
问题描述：
9（3a-2b）²-4（a+3b）²
答
9(3a-2b)²-4(a+3b)²
=[3(3a-2b)]²-[2(a+3b)]²
=[3(3a-2b)+2(a+3b)][3(3a-2b)-2(a+3b)]
=11a(7a-12b)