已知x^2+y^2=7,xy=-2.求5X^2-3(XY-Y^2)-11XY-2(-X^2-2Y^2)的值
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人气：371 ℃ 时间：2020-07-13 08:48:17
解答
5x²-3(xy-y²)-11xy-2(-x²-2y²)
=5x²-3xy+3y²-11xy+2x²+4y²
=7x²+7y²-14xy
=7(x²+y²)-14xy
=7×7-14×(-2)
=49+28
=77
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