Answer
$\cosh(-x)= \cosh x$
Work Step by Step
Since, we know $\cosh(x) = \dfrac{e^{x} + e^{-x}}{2}$
Thus, $\cosh(-x) =\dfrac{e^{-x} + e^{-(-x)}}{2}$
or, $ =\dfrac{e^{-x} + e^{x}}{2}$
or, $= \cosh x$
Hence, it has been proved that $\cosh(-x)= \cosh x$
