1. Вычислите: a) sin 240°; б) cos(-$$\frac{5\pi}{6}$$); в) 3 cos$$\frac{\pi}{4}$$ - sin$$\frac{\pi}{6}$$

a) sin 240° = sin (180° + 60°) = -sin 60° = -$$\frac{\sqrt{3}}{2}$$$ б) cos(-$$\frac{5\pi}{6}$$) = cos(-150°) = cos(150°) = cos(180° - 30°) = -cos 30° = -$$\frac{\sqrt{3}}{2}$$$ в) 3 cos$$\frac{\pi}{4}$$ - sin$$\frac{\pi}{6}$$ = 3 cos 45° - sin 30° = 3 * $$\frac{\sqrt{2}}{2}$$ - $$\frac{1}{2}$$ = $$\frac{3\sqrt{2} - 1}{2}$$$ Ответ: a) -$$\frac{\sqrt{3}}{2}$$; б) -$$\frac{\sqrt{3}}{2}$$; в) $$\frac{3\sqrt{2} - 1}{2}$$