[a-﹙2ab-b2﹚/a]·[﹙a2+ab﹚/﹙a2-b2﹚]
=[（a²-2ab+b²﹚/a]·[a﹙a+b﹚]/[(a+b)(a-b)]
=(a-b)²/a*a/(a-b)
=a-b
∵-3