已知x-2y=15,xy=-25,求x^2+4y^2-1的值

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已知x-2y=15,xy=-25,求x^2+4y^2-1的值已知x-2y=15,xy=-25,求x^2+4y^2-1的值已知x-2y=15,xy=-25,求x^2+4y^2-1的值x=2y+15(2y

已知x-2y=15,xy=-25,求x^2+4y^2-1的值
已知x-2y=15,xy=-25,求x^2+4y^2-1的值

已知x-2y=15,xy=-25,求x^2+4y^2-1的值
x=2y+15
(2y+15)*y=-25
y=-5,x=5或y=-2.5,x=10
所以x^2+4y^2-1=124

已知x-2y=15,xy=-25得（x-2y）（x-2y）=225=x^2+4y^2-4xy可得x^2+4y^2-1=4xy+225-1=124

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