Answer
(a). $f'(x) = \frac{e^x−e^{−x}}
{2}$ , which is zero when $e^x = e^{−x}$ or
$x =-x$, so only for $x = 0$.
(b). There is a local (and absolute) minimum at $x = 0$.
Work Step by Step
See the graph for explanation of the above.
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