a+1/a=3 a^2+1/a^2+2=9 a^2+1/a^2=7 a^4+1=7a^2 a的2次幂 / a的4次幂+a的2次幂+1 =a^2/(a^4+1+a^2)=a^2/(7a^2+a^2)=1/8