a是方程x^2-3x+1=0的根
a^2-3a+1=0
a^2+1=3a
a+1/a=3
2a^2-5a-2+3/(a^2+1)
=2(a^2-3a+1)+a-4+3/3a
=a-4+1/a
=(a+1/a)-4
=3-4
=-1