\[\boxed{\mathbf{89}.}\]
\[1)\ \sqrt{2x - 1} = 5;\ \ 2x - 1 \geq 0;\ \]
\[\ x \geq 0,5.\]
\[2x - 1 = 25\]
\[2x = 26\]
\[x = 13.\]
\[Ответ:x = 13.\]
\[2)\ \sqrt{4 - 0,5x} = 2;\ \ \ \]
\[4 - 0,5x \geq 0;\ \ x \leq 8.\]
\[4 - 0,5x = 4\]
\[0,5x = 0\]
\[x = 0.\]
\[Ответ:x = 0.\]