(3a-2b)(2b+3a)-（2a-3b）^2=(3a-2b)(2b+3a-3b+2a)=(3a-2b)(-b+5a)=15a^2-13ab+2b^2
ab-[3a^2b-(2/3ab+4a^2b)]-(2ab+a^2b)=ab-ab[3a-2/3-4a]-ab(2+a)=ab(1-3a+2/3+4a-2-a)=ab(-1/3)=-1/3ab