已知x^2-y^2=24,x-y=-6,求代数式5x+5y的值.

已知x^2-y^2=24,x-y=-6,求代数式5x+5y的值.急啊,快快,请高手指教啊```````

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解：（x-y)(x+y)=24 6(x+y)=24 x+y=-4 5x+5y=5(x+y)=-20

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