若a方减去3a-1等于0,求a四次方+a四次方分之一的值

a^2-3a-1=0
a-3-1/a=0
a-1/a=3
a^4+1/a^4
=(a^2+1/a^2)^2-2
=[(a+1/a)^2-2]^2-2
=[(a-1/a)^2+4-2]^2-2
=(9+4-2)^2-2
=119