a^2/[a^4+a^2+1]=?
[a+1/a]^2=a^2+1/a^2+2=25
a^2+1/a^2=23
[a^4+a^2+1]/a^2=a^2+1/a^2+1=23+1=24
所以：a^2/[a^4+a^2+1]=1/24