9.125. $y=\sqrt{\log _{\frac{1}{3}} \log _{3}|x-3|}$.
## Solution.

The domain of definition of the given function will be those values of $x$ for which the inequality

$$
\begin{aligned}
& \log _{\frac{1}{3}} \log _{3}|x-3| \geq 0 \Leftrightarrow 0 1 }
\end{array} \Leftrightarrow \left\{\begin{array} { l } 
{ - 3 \leq x - 3 \leq 3 , } \\
{ [ \begin{array} { l } 
{ x - 3 > 1 , } \\
{ x - 3 4 \\
x<2
\end{array}\right.}
\end{array}\right.\right.\right.
\end{aligned}
$$

Answer: $x \in[0 ; 2) \cup(4 ; 6]$.