已知x^2 -5x+1=0,求 x^3-4x^2 -4x-1

问题描述:

已知x^2 -5x+1=0,求 x^3-4x^2 -4x-1

因为x²-5x+1=0
所以x²=5x-1
所以,x³-4x²-4x-1
=x(5x-1)-4(5x-1)-4x-1
=5x²-x-20x+4-4x-1
=5(5x-1)-25x+3
=25x-5-25x+3
=-2

望采纳,谢谢!