\[y = \sin{2x};\ \ \ x = a.\]
\[1)\ a = \frac{\pi}{4}:\]
\[\sin\left( 2 \bullet \frac{\pi}{4} \right) = \sin\frac{\pi}{2} = 1;\]
\[2)\ a = \frac{\pi}{3}:\]
\[\sin\frac{2\pi}{3} = \sin\frac{\pi}{3} = \frac{\sqrt{3}}{2};\]
\[3)\ a = - \frac{2\pi}{3}:\]
\[\sin\left( - 2 \bullet \frac{2\pi}{3} \right) = \sin\left( - \frac{4\pi}{3} \right) =\]
\[= \sin\frac{2\pi}{3} = \frac{\sqrt{3}}{2};\]
\[4)\ a = - \frac{5\pi}{6}:\]
\[\sin\left( - 2 \bullet \frac{5\pi}{6} \right) = \sin\left( - \frac{5\pi}{3} \right) =\]
\[= \sin\frac{\pi}{3} = \frac{\sqrt{3}}{2}.\]