
\begin{enumerate}
\item $\cos\dfrac{215\pi}{6}=\cos\left(-\dfrac{\pi}{6}\right)=\cos\dfrac{\pi}{6}=\dfrac{\sqrt3}{2}$.

\item $\sin\dfrac{316\pi}{6}=\sin \dfrac{2\pi}{3}=\dfrac{1}{2}$.
\end{enumerate}
