cosh ( θ ) = e x + e − x 2 {\displaystyle \cosh(\theta )={\frac {e^{x}+e^{-x}}{2}}}
cosh ( x ) = ∑ k = 0 ∞ x 2 k ( 2 k ) ! {\displaystyle \cosh(x)=\sum _{k=0}^{\infty }{\frac {x^{2k}}{(2k)!}}}
cosh ( x ) = cos ( i x ) {\displaystyle \cosh(x)=\cos(ix)}
