\[\sqrt{x^{2} - 4} + \sqrt{1 - \frac{1}{25}x^{2}}\]

\[\left\{ \begin{matrix}
(x + 2)(x - 2) \geq 0 \\
(x + 5)(x - 5) \leq 0 \\
\end{matrix} \right.\ \]
\[(x + 2)(x - 2) \geq 0\]

\[x \leq - 2;\ \ x \geq 2.\]
\[(x + 5)(x - 5) \leq 0\]

\[- 5 \leq x \leq 5.\]
\[\left\{ \begin{matrix}
x \leq - 2;\ \ x \geq 2 \\
- 5 \leq x \leq 5\ \ \ \ \ \ \\
\end{matrix} \right.\ \]

\[D(y) = \lbrack - 5;\ - 2\rbrack \cup \lbrack 2;5\rbrack.\]