Exercício Resolvido de Funções Complexas
c)
\( \cos {iz}=\cosh z \)
Coseno é dado por
\[ \bbox[#99CCFF,10px]
{\cos z=\frac{\operatorname{e}^{iz}+\operatorname{e}^{-iz}}{2}}
\]
\[
\begin{gather}
\cos iz=\frac{\operatorname{e}^{i.iz}+\operatorname{e}^{-i.iz}}{2}=\frac{\operatorname{e}^{i^{2}z}+\operatorname{e}^{-i^{2}z}}{2}=\frac{\operatorname{e}^{-z}+\operatorname{e}^{z}}{2}
\end{gather}
\]
\[ \bbox[#FFCCCC,10px]
{\cos iz=\cosh z}
\]