Derivative of Constant to Power of Function

Theorem
Let $u$ be a differentiable real function of $x$.

Let $a \in \R_{>0}$.

Let $a^u$ be $a$ raised to the power of $u$.

Then:
 * $\map {\dfrac \d {\d x} } {a^u} = a^u \ln a \dfrac {\d u} {\d x}$