A-｛B+[A-2B-（A+B）]｝=A-﹛B+[A-2B-A-B]﹜=A-﹛B+A-2B-A-B﹜=A+2B∵A=5x的三次方+3y的二次方,B=3x的三次方-4y的二次方∴A+2B=5X³+3Y²+2﹙3X³-4Y²﹚=5X³+3Y²+6X³-8Y²=11X&...