a是方程X2-3X+1=0的解
所以a^2-3a+1=0
即3a=a^2+1
(2a^5-6a^4+2a^3-a^2-1)/3a
=[2a^3(a^2+1)-(a^2+1)]/(a^2+1) - 6a^4 / 3a
=2a^3-1-2a^3
=-1