\[\boxed{\text{246}\text{\ (246)}\text{.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ f(x) = \frac{x - 5}{(x - 2)(x - 1)}\]
\[2)\ f(x) = \frac{\sqrt{x - 5}}{x^{2} + 1}\]
\[3)\ f(x) = \frac{\sqrt{10 - x}}{5 \cdot (x + 1)}\]
\[4)\ f(x) = \sqrt{x + 4} + \sqrt{- 4 - x}\ \]