若x^2-x-1=0求x^5-5x+27的值
问题描述：
若x^2-x-1=0求x^5-5x+27的值
答
x^5-5x+27
=x^5-x^4-x^3+x^4+x^3-5x+27
=x^3(x^2-x-1)+x^4-x^3-x^2+2x^3+x^2-5x+27
=x^4-x^3-x^2+2x^3+x^2-5x+27
=x^2(x^2-x-1)+2x(x^2-x-1)+3x^2-3x+27
=3(x^2-x-1)+30
=30