\[y = \sqrt{|5 - x| - 8}\ \]
\[|5 - x| - 8 \geq 0\]
\[|5 - x| \geq 8\ \ \ \ \ \ \ \ \]
\[5 - x \geq 8\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 5 - x \leq - 8\]
\[x \leq - 3\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x \geq 13\]
\[D(y) = ( - \infty; - 3\rbrack \cup \lbrack 13; + \infty).\]