若P=a²+3ab+b²,Q=a²-3ab+b²,则代数式P-[Q-2P-（-P-Q）]=___.

若P=a²+3ab+b²,Q=a²-3ab+b²,则代数式P-[Q-2P-（-P-Q）]=___.
若P=a²+3ab+b²,Q=a²-3ab+b²,则代数式P-[Q-2P-（-P-Q）]=___.

若P=a²+3ab+b²,Q=a²-3ab+b²,则代数式P-[Q-2P-（-P-Q）]=___.
P-[Q-2P-（-P-Q）]=P-[Q-2P+P+Q]=P-(2Q-P)=P-2Q+P=2P-2Q=2*(P-Q)=2[(a^2+3ab+b^2)-(a^2-3ab+b^2)]=2[a^2+3ab+b^2-a^2+3ab-b^2]=12ab

P-[Q-2P-（-P-Q）]=2(P-Q)=12ab

P=a²+3ab+b²=（a+b）^2+ab Q=a²-3ab+b²=（a+b）^2-5ab，P-Q=（a+b）^2+ab -{（a+b）^2-5ab}=6ab
P-[Q-2P-（-P-Q）]=P-(Q-2P+P+Q)=P-Q+2P-P-Q=2P-2Q=2(P-Q)=2X6ab=12ab