a是方程x²-3x+1=0的根则,a²-3a+1=0 得,a²-3a=-1 ,a²+1=3a ,a+1/a=32a²-5a+2+3/a²+1=2a²-6a+a+2+3/(3a)=2(a²-3a)+a+2+1/a=-2+a+2+1/a=a+1/a=3
