Derivative of Power of Function/Proof 2

Theorem
Let $u \left({x}\right)$ be a differentiable real function.

Let $n$ be a real number such that $n \ne -1$.

Then:
 * $D_x \left({u \left({x}\right)^n}\right) = n \left({u \left({x}\right)}\right)^{n - 1} D_x u \left({x}\right)$