a是方程x2-3x+1=0的根所以a^2-3a+1=0所以a^2+1=3aa3-2a2-5a+1/a2+1=(a^3-3a^2+a^2-5a+1)/(a^2+1)=[a(a^2-3a)+a^2-5a+1]/(a^2+1)=(-a+a^2-5a+1)/(a^2+1)=(a^2+1-6a)/(a^2+1)=(3a-6a)/3a=-3a/3a=-1
