\[\sqrt{6x + 1} + \frac{3}{\sqrt{5 - x}}\]
\[\ \left\{ \begin{matrix} 6x + 1 \geq 0 \\ 5 - x > 0\ \ \\ \end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix} 6x \geq - 1 \\ - x > - 5 \\ \end{matrix} \right.\ \Longrightarrow \left\{ \begin{matrix} x \geq - \frac{1}{6} \\ x < 5\ \ \ \\ \end{matrix} \right.\ \ \]
\[Ответ:x \in \left\lbrack - \frac{1}{6};5 \right).\]