삼각함수 값 계산

[출제의도] 삼각함수 이해하기 $\displaystyle \sin \frac{5}{6} \pi = \sin \left( \pi - \frac{\pi}{6} \right) = \sin \frac{\pi}{6} = \frac{1}{2}$, $\displaystyle \mathrm{\cos} \left( - \frac{8}{3} \pi \right) = \cos \frac{8}{3} \pi = \cos \left( 2 \pi + \frac{2}{3} \pi \right)$ $\displaystyle = \cos \frac{2}{3} \pi = \cos \left( \pi - \frac{\pi}{3} \right)$ $\displaystyle = \mathit{-} \cos \frac{\pi}{3} = \mathit{-} \frac{1}{2}$ 이므로 $\displaystyle \mathrm{\sin} \frac{5}{6} \pi + \cos \left( - \frac{8}{3} \pi \right)$$\displaystyle = \frac{1}{2} - \frac{1}{2} = 0$이다.