\[\cos x = - \frac{\sqrt{3}}{2};\ \]
\[\log_{2}(x - 1) < 3.\ \]
\[1)\ \cos x = - \frac{\sqrt{3}}{2}\]
\[x = \pm \frac{5\pi}{6} + 2\pi\text{n.}\]
\[2)\ \log_{2}(x - 1) < 3\]
\[0 < x - 1 < 8\]
\[1 < x < 9.\]
\[Ответ:\ \ \frac{5\pi}{6};\ \frac{7\pi}{6};\ \frac{17\pi}{6}.\]