Cho

B

- Hướng dẫn giải

Đáp án B

$$\begin{gathered} {\log }_{9}147={\log }_{3^2}\left({3.7}^2\right)=\frac{1}{2}{\log }_3\left({3.7}^2\right) \\ =\frac{1}{2}\left(1+2{\log }_{3}7\right) \end{gathered}$$

Ta có ${\log }_{3}7=\frac{{\log }_{2}7}{{\log }_{2}3}=\frac{b}{a}$.

$\Rightarrow {\log }_{9}147=\frac{1}{2}\left(1+2.\frac{b}{a}\right)=\frac{a+2b}{2a}.$