a²-b²=（a²-ab）+（ab-b²）=9+6=15 a²-3ab+2b²=（a²-ab）-2（ab-b²）=9-2×6=9-12=-3 ~一刻永远523为你解答,祝你学习进步~~~~如果你认可我的回答,请及时点击【采纳为满意回...