\[f(x) = \sqrt{x - 1} + \frac{x + 3}{x - 10},\ \ \]
\[\left\{ \begin{matrix}
x - 1 \geq 0 \\
x
eq 10\ \ \ \ \ \ \\
\end{matrix} \right.\ \text{\ \ \ \ \ \ \ }\left\{ \begin{matrix}
x \geq 1\ \ \ \\
x
eq 10 \\
\end{matrix} \right.\ \]
\[D(f) = \lbrack 1;10) \cup (10;\ + \infty)\]