Answer
$-1.11$
Work Step by Step
Note that $\cot {x}=\frac{1}{\tan{(x)}}$.
Hence, $\cot^{-1}{x}=\tan^{-1} {\left(\frac{1}{x}\right)}$.
Use a calculator in radian mode and round the result to decimal places to obtain
$\cot^{-1}{(-\frac{1}{2})}=\tan^{-1} \left(\frac{1}{-\frac{1}{2}}\right)\approx-1.11$