# For $0 < x \leq \pi, \sin h^{-1} (\cot x)=$

$\begin {array} {1 1} (a)\;\log (\cot \frac{x}{2}) & \quad (b)\;\log (\tan \frac{x}{2}) \\ (c)\; \log (1+ \cot x) & \quad (d)\;\log (1+ \tan x) \end {array}$

$(a)\;\log (\cot \frac{x}{2})$