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若xy=-2,x+y=3,求值:﹙1﹚﹙xy-4x﹚+x-3y;﹙2﹚﹙3xy+10y﹚+[5x﹣﹙2xy+2y-3x﹚]
人气:432 ℃ 时间:2019-10-19 15:21:43
解答
﹙1﹚﹙xy-4x﹚+x-3y
=xy-3x-3y
=xy-3(x+y)
=-2-3*3
=-11
﹙2﹚﹙3xy+10y﹚+[5x﹣﹙2xy+2y-3x﹚]
=3xy+10y+5x-2xy-2y+3x
=xy+8y+8x
=xy+8(x+y)
=-2+8*3
=22
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