\[1)\cos\left( \arcsin\frac{3}{5} \right) =\]
\[= + \sqrt{1 - \sin^{2}\left( \arcsin\frac{3}{5} \right)} =\]
\[= \sqrt{1 - \left( \frac{3}{5} \right)^{2}} = \sqrt{\frac{25}{25} - \frac{9}{25}} =\]
\[= \sqrt{\frac{16}{25}} = \frac{4}{5}.\]
\[2)\sin\left( \arccos\left( - \frac{5}{13} \right) \right) =\]
\[= + \sqrt{1 - \cos^{2}\left( \arccos\left( - \frac{5}{13} \right) \right)} =\]
\[= \sqrt{1 - \left( - \frac{5}{13} \right)^{2}} = \sqrt{\frac{169}{169} - \frac{25}{169}} =\]
\[= \sqrt{\frac{144}{169}} = \frac{12}{13}.\]