Question

已知x的二次方+4x-1=0,求2x的四次方+8x的三次方-4x的二次方-8x+1的值

Answer 1

x^2+4x-1=0

x^2+4x=1

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

=-2+1

=-1