已知x^2+y^2=7,xy=-2,5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)的值
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已知x^2+y^2=7,xy=-2,5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)的值
已知x^2+y^2=7,xy=-2,5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)的值
已知x^2+y^2=7,xy=-2,5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)的值
5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)
=x²+y²-14xy
=7+14×2
=35
=x^2-14xy+y^2=7-14*(-2)=35
答案是35
展括号,合并同类项,后代入已知数据
5x^2-3xy-y^2-11xy+(-4x^2)-(-2y^2)=(x^2+y^2)-14xy=7-(-28)=35