\[( - \pi;\ 2\pi).\]
\[1)\ ctg\ x = 1\]
\[x = \frac{\pi}{4} + \pi n.\]
\[Ответ:\ - \frac{3\pi}{4};\ \frac{\pi}{4};\ \frac{5\pi}{4}.\]
\[2)\ tg\ x = \sqrt{3}\]
\[x = \frac{\pi}{3} + \pi n.\]
\[Ответ:\ - \frac{2\pi}{3};\ \frac{\pi}{3};\ \frac{4\pi}{3}.\]
\[3)\ ctg\ x = - \sqrt{3}\]
\[x = - \frac{\pi}{6} + \pi n.\]
\[Ответ:\ - \frac{\pi}{6};\ \frac{5\pi}{6};\ \frac{11\pi}{6}.\]
\[4)\ tg\ x = - 1\]
\[x = - \frac{\pi}{4} + \pi n.\]
\[Ответ:\ - \frac{\pi}{4};\ \frac{3\pi}{4};\ \frac{7\pi}{4}.\]