a²-3a+1=0
所以a²+1=3a
a²-3a=-1
所以原式=(3a^4-7a³-3a²+a)/(3a)
=(3a³-7a²-3a+1)/3
=[(3a³-9a²)+(2a²-6a)+3a+1)/3
=[3a(a²-3a)+2(a²-3a)+3a+1]/3
=(-3a-2+3a+1)/3
=-1/3