\[\sqrt{2 - 5x}\ \]
\[ОДЗ:2 - 5x \geq 0\]
\[\ \ \ \ \ \ \ \ \ - 5x \geq - 2\]
\[\ \ \ \ \ \ \ \ \ \ \ \ \ x \leq 0,4\ \]
\[Ответ:x \in ( - \infty;0,4\rbrack\text{.\ }\]