已知a^2-5a-1=0,则代数式(a^4+a^2+1)/a^2的值是

a^2-5a-1=0 等式两边同除a：
a-5-1/a=0
a-1/a=5
(a-1/a)^2=5^2
a^2-2+1/a^2=25
a^2+1/a^2=27
(a^4+a^2+1)/a^2
=a^2+1+1/a^2
=a^2+1/a^2+1
=27+1
=28