x^2+4x-1=0求2x^4+8x^3-4x^2-8x+1
问题描述:
x^2+4x-1=0求2x^4+8x^3-4x^2-8x+1
答
x^2+4x=1
所以
2x^4+8x^3-4x^2-8x+1
=2x^2(x^2+4x)-4x^2-8x+1
=2x^2-4x^2-8x+1
=-2x^2-8x+1
=-2(x^2+4x)+1
=-1