\[\boxed{\mathbf{1176}\mathbf{.}}\]
\[1)\sin\left( \arccos\frac{2}{3} \right) =\]
\[= \sqrt{1 - \cos^{2}\left( \arccos\frac{2}{3} \right)} =\]
\[= \sqrt{1 - \left( \frac{2}{3} \right)^{2}} = \sqrt{\frac{9}{9} - \frac{4}{9}} =\]
\[= \sqrt{\frac{5}{9}} = \frac{\sqrt{5}}{3}\]
\[2)\sin\left( \arccos\left( - \frac{1}{2} \right) \right) =\]
\[= \sqrt{1 - \cos^{2}\left( \arccos\left( - \frac{1}{2} \right) \right)} =\]
\[= \sqrt{1 - \left( - \frac{1}{2} \right)^{2}} = \sqrt{\frac{4}{4} - \frac{1}{4}} =\]
\[= \sqrt{\frac{3}{4}} = \frac{\sqrt{3}}{2}\]