5x2-3xy-4y2-11xy+(-7x2)-(-2y2),其中x2+y2=7,xy=-2,求值
人气：451 ℃ 时间：2019-11-09 12:44:57
解答
5x2-3xy-4y2-11xy+(-7x2)-(-2y2),
=5x2-3xy-4y2-11xy-7x2+2y2
=-2x2-14xy-2y2
=-2(x2+y2)-14xy
=-14+28
=14
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