Вычислить: 1) cos 765°; 2) sin \frac{19\pi}{6}

1) cos 765° = cos (720° + 45°) = cos (2 * 360° + 45°) = cos 45° = \frac{\sqrt{2}}{2} 2) sin \frac{19\pi}{6} = sin (3\pi + \frac{\pi}{6}) = sin (\pi + 2\pi + \frac{\pi}{6}) = sin (\pi + \frac{\pi}{6}) = -sin \frac{\pi}{6} = -\frac{1}{2} **Ответ:** 1) \frac{\sqrt{2}}{2}; 2) -\frac{1}{2}