Solve this

$y=\log _{a} x=\frac{\log _{e} x}{\log _{e} a}$

$\therefore \frac{\mathrm{dy}}{\mathrm{dx}}=\frac{1}{\log _{e} \mathrm{a}} \cdot \frac{1}{\mathrm{x}}$

$=\frac{1}{x \log _{e} a}$ (Ans)