已知x^2+4x-1=0,求2x^4+8x^3-4x^2-8x+1的值.

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已知x^2+4x-1=0,求2x^4+8x^3-4x^2-8x+1的值.
已知x^2+4x-1=0,求2x^4+8x^3-4x^2-8x+1的值.

已知x^2+4x-1=0,求2x^4+8x^3-4x^2-8x+1的值.
2x^4+8x^3-4x^2-8x+1
=2x^4+8x^3-2x^2-2x^2-8x+1
=2x^2(x^2+4x-1)-2x^2-8x+1
=2x^2(x^2+4x-1)-2(x^2+4x-1)-1 [x^2+4x-1=0]
=-1

x^2+4x-1=0,求2x^4+8x^3-4x^2-8x+1
= 2x^2(x^2+4x-1)-2x^2-8x+1
= 2x^2(x^2+4x-1)-2(x^2+4x-1)-1
=-1