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先化简再求值,3x^y-[2x^2y-3(2xy-x^2y)-xy]其中x=-1,y=-2
人气：278 ℃　时间：2019-08-21 21:01:01
解答
3x^y漏掉了一个2次方吧
3x^2y-[2x^2y-3(2xy-x^2y)-xy]
=3x^2y-2x^2y+3(2xy-x^2y)+xy
=3x^2y-2x^2y+6xy-3x^2y+xy
=3x^2y-3x^2y-2x^2y+6xy+xy
=-2x^2y+7xy
=xy(-2x+7)
=2*(2+7)
=18
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