Precalculus (10th Edition)

$-6$
We know that $\cot$ has a period of $\pi$, hence $\cot(\theta)=\cot(\theta+k\pi)$ where $k$ is an integer. Therefore, $\cot(\theta)+\cot(\theta-\pi)+\cot(\theta-2\pi)\\ =\cot(\theta)+\cot(\theta)+\cot(\theta)\\ =-2+(-2)+(-2)\\ =-6$