\[\begin{array}{l} \sinh x = \sum\limits_{k = 0}^{ + \infty } {\frac{{{x^{2k + 1}}}}{{\left( {2k + 1} \right)!}}} \hfill \\ \cosh x = \sum\limits_{k = 0}^{ + \infty } {\frac{{{x^{2k}}}}{{\left( {2k} \right)!}}} \hfill \\ \end{array}\]