Find the principal value of each of the following :

$\cot \left(\tan ^{-1} x+\cot ^{-1} x\right)=\cot \left(\frac{\pi}{2}\right)\left[\right.$ Formula: $\left.\tan ^{-1} x+\cot ^{-1} x=\frac{\pi}{2}\right]$

Putting value of $\cot \left(\frac{\pi}{2}\right)$

$=0$