在由正数组成的等比数列 $\left\{a_{n}\right\}$ 中, 若 $a_{4} a_{5} a_{6}=3, \log _{3} a_{1}+\log _{3} a_{2}+\log _{3} a_{8}+\log _{3} a_{9}$ 的值为(
解析 $\because a_{4} a_{6}=a_{5}^{2}, \therefore a_{4} a_{5} a_{6}=a_{5}^{3}=3$, 得 $a_{5}=3 \frac{1}{3}$.
$\because a_{1} a_{9}=a_{2} a_{8}=a_{5}^{2}$

$\therefore \log _{3} a_{1}+\log _{3} a_{2}+\log _{3} a_{8}+\log _{3} a_{9}=\log _{3}\left(a_{1} a_{2} a_{8} a_{9}\right)$

$=\log _{3} a_{5} 4=\log _{3} 3 \frac{4}{3}=\frac{4}{3}$.