18. \( \sin(-316^\circ), \cos(-\frac{17\pi}{7}), tg 289^\circ, ctg(-\frac{15\pi}{6}) \)

* \( \sin(-316^\circ) = -\sin 316^\circ = -\sin(360^\circ - 44^\circ) = \sin 44^\circ \) * \( \cos(-\frac{17\pi}{7}) = \cos(\frac{17\pi}{7}) = \cos(2\pi + \frac{3\pi}{7}) = \cos(\frac{3\pi}{7}) \) * \( tg 289^\circ = tg(270^\circ + 19^\circ) = -ctg 19^\circ \) * \( ctg(-\frac{15\pi}{6}) = -ctg(\frac{15\pi}{6}) = -ctg(\frac{5\pi}{2}) = 0 \)