$\begin{array}{l}
\sin 2x = - \frac{1}{2} = \sin \left( { - \frac{\pi }{6}} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
2x = - \frac{\pi }{6} + k2\pi \\
2x = \frac{{7\pi }}{6} + k2\pi
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = - \frac{\pi }{{12}} + k\pi \\
x = \frac{{7\pi }}{{12}} + k\pi
\end{array} \right.\\
Ma\,0 < x < \pi \Leftrightarrow \left[ \begin{array}{l}
0 < - \frac{\pi }{{12}} + k\pi < \pi \\
0 < \frac{{7\pi }}{{12}} + k\pi < \pi
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
k = 1\\
k = 0
\end{array} \right.\\
Co\,2\,nghiem.
\end{array}$
