Prove that the function f(x) = cosh(x)+ cos(x) is strictly increasing for non-negative x

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I know that using the mean value theorem I should get $f'(x) =$ sinh$(x)$ - sin$(x)$, but from that on I have no ideas on how to show that $f'(x) > 0$ in the specified interval. Basic trigonometric identities may be used. Also any methods other than the mean value theorem will be welcomed.

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That function, $f'(x)$, is zero at $x=0$. Can you show that its derivative - that is, $f''(x)$, is positive on $x>0$?