thb67
§
\[\begin{array}{l}
\sinh x = \sum\limits_{k = 0}^{ + \infty } {\frac{{{x^{2k + 1}}}}{{\left( {2k + 1} \right)!}}} \hfill \\
\cosh x = \sum\limits_{k = 0}^{ + \infty } {\frac{{{x^{2k}}}}{{\left( {2k} \right)!}}} \hfill \\
\end{array}\]
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