\[\sqrt{2x + 1} = \sqrt{2 \cdot 5 - 1}\]
\[\sqrt{2x + 1} = \sqrt{9}\]
\[2x + 1 = 9\]
\[2x = 9 - 1\]
\[2x = 8\]
\[x = 4.\]
\[Ответ:x = 4.\ \]