Đáp án:
\[\left[ \begin{array}{l}
x = k4\pi \\
x = \frac{{10\pi }}{3} + k4\pi
\end{array} \right.\]
Giải thích các bước giải:
9,
\[\begin{array}{l}
\sin \left( {\frac{x}{2} - \frac{\pi }{3}} \right) = - \frac{{\sqrt 3 }}{2}\\
\Leftrightarrow \sin \left( {\frac{x}{2} - \frac{\pi }{3}} \right) = \sin \left( { - \frac{\pi }{3}} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
\frac{x}{2} - \frac{\pi }{3} = - \frac{\pi }{3} + k2\pi \\
\frac{x}{2} - \frac{\pi }{3} = \pi - - \frac{\pi }{3} + k2\pi
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
\frac{x}{2} = k2\pi \\
\frac{x}{2} = \frac{{5\pi }}{3} + k2\pi
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x = k4\pi \\
x = \frac{{10\pi }}{3} + k4\pi
\end{array} \right.
\end{array}\]
