Calculate \( \frac{du}{dx} \) where \( u = e^{\cos x} \). Use the chain rule again: \( \frac{d}{dx}[e^{\cos x}] = e^{\cos x} \cdot (-\sin x) \).
Combine the results: \( \frac{d}{dx}[\cot^{-1}(e^{\cos x})] = -\frac{1}{1+(e^{\cos x})^2} \cdot e^{\cos x} \cdot (-\sin x) \). Simplify to get the final expression.