Derivative of Arccotangent Function/Corollary

Corollary to Derivative of Arccotangent Function
Let $x \in \R$.

Let $\operatorname{arccot} \left({\dfrac x a}\right)$ be the arccotangent of $\dfrac x a$.

Then:
 * $\dfrac {\mathrm d \left({\operatorname{arccot} \left({\frac x a}\right) }\right)} {\mathrm d x} = \dfrac {-a} {a^2 + x^2}$