x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值

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x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值
x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值

x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值
5x² - 3xy - 4y² - 11xy - 7x² + 2y²
= -2x² - 2y² -14xy
= -2(x² + y²) -14xy
= -2×7 - 14×(-2)
= -14 + 28
= 14

14，不过楼主题应该出错了

5x^2-3xy-4y^2-11xy-7x^2+2y^2
=-2x^2-14xy-2y^2
=-2(x^2+y^2)-14xy
因为x^2+y^2=7,xy=-2
所以原式=-2*7-14*（-2）=14

14

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