17. \( \cos 312^\circ, \sin(-\frac{15\pi}{8}), ctg 308^\circ, tg(\frac{10\pi}{3}) \)

* \( \cos 312^\circ = \cos(360^\circ - 48^\circ) = \cos 48^\circ \) * \( \sin(-\frac{15\pi}{8}) = -\sin(\frac{15\pi}{8}) = -\sin(2\pi - \frac{\pi}{8}) = \sin(\frac{\pi}{8}) \) * \( ctg 308^\circ = ctg(360^\circ - 52^\circ) = -ctg 52^\circ \) * \( tg(\frac{10\pi}{3}) = tg(3\pi + \frac{\pi}{3}) = tg(\pi + \frac{\pi}{3}) = tg(\frac{\pi}{3}) \)