# Very basic derivative question

Why is the derivative of $e^x + e^{-x}$ equal to $e^x - e^{-x}$ ?

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## 1 Answer

By the chain rule, the derivative of $e^{f(x)}$ is $f'(x)e^{f(x)}$. Hence, $$\frac{d}{dx}[e^{x} + e^{-x}] = \left[\frac{d}{dx}(x)\right]\cdot e^{x} + \left[\frac{d}{dx}(-x)\right]\cdot e^{-x} = e^{x} - e^{-x}$$

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