\[\begin{array}{l}
y = \sin 2x,\,\,\,x \in \left[ { - \frac{\pi }{2};\,\,\frac{\pi }{2}} \right]\\
\Rightarrow y' = 2\cos 2x = 0\\
\Leftrightarrow \cos 2x = 0 \Leftrightarrow 2x = \frac{\pi }{2} + k\pi \\
\Leftrightarrow x = \frac{\pi }{4} + \frac{{k\pi }}{2}\,\,\left( {k \in Z} \right)\\
x \in \left[ { - \frac{\pi }{2};\,\,\frac{\pi }{2}} \right] \Rightarrow x \in \left\{ { - \frac{\pi }{4};\,\,\frac{\pi }{4}} \right\}\\
Bang\,\,bien\,\,thien:\\
x\,\,\,\,\,\,\,\,\,\,\, - \frac{\pi }{2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, - \frac{\pi }{4}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{\pi }{4}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\frac{\pi }{2}\\
f'\left( x \right)\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, - \,\,\,\,\,\,\,\,\,\,\,\,0\,\,\,\,\,\,\,\,\,\,\,\, + \,\,\,\,\,\,\,\,0\,\,\,\,\,\,\,\,\, -
\end{array}\]
