- Hướng dẫn giải

${\log }_3\left(x\right).{\log }_9\left(x\right).{\log }_{27}\left(x\right).{\log }_{81}\left(x\right)=\frac{2}{3}$

$$\begin{gathered} {\log }_3\left(x\right).\frac{1}{2}{\log }_3\left(x\right).\frac{1}{3}{\log }_3\left(x\right).\frac{1}{4}{\log }_3\left(x\right)=\frac{2}{3} \\ \iff {\left({\log }_3\left(x\right)\right)}^4=16 \\ \iff \left\{\begin{array}{l}{\log }_3\left(x\right)=2\\ {\log }_3\left(x\right)=-2\end{array}\right. \\ \iff \left\{\begin{array}{l}x=9\\ x=\frac{1}{9}\end{array}\right. \end{gathered}$$

Tổng các nghiệm bằng $\frac{82}{9}$

Đáp án cần chọn là A