a是方程的根
所以a²-3a+1=0
所以a²+1=3a
且a²=3a-1
原式=2(3a-1)-5a-2+3/(3a)
=6a-2-5a-2+1/a
=a-4+1/a
=(a²+1)/a-4
=3a/a-4
=3-4
=-1