若一元二次方程x²+2x-1=0,则2x²+4x值为
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![若一元二次方程x²+2x-1=0,则2x²+4x值为](/uploads/image/z/578084-68-4.jpg?t=%E8%8B%A5%E4%B8%80%E5%85%83%E4%BA%8C%E6%AC%A1%E6%96%B9%E7%A8%8Bx%26%23178%3B%2B2x-1%3D0%2C%E5%88%992x%26%23178%3B%2B4x%E5%80%BC%E4%B8%BA)
若一元二次方程x²+2x-1=0,则2x²+4x值为
若一元二次方程x²+2x-1=0,则2x²+4x值为
若一元二次方程x²+2x-1=0,则2x²+4x值为
2x²+4x
=2x²+4x-2+2
=2(x²+2x-1)+2
∵x²+2x-1=0
∴原式=2
x²+2x-1=0
x²+2x=1
x(x+2)=1
2x²+4x=2x(x+2)=2