(1)

\begin{align*} i\sin x & =i\frac{e^{ix}-e^{-ix}}{2i}\\ & =\frac{e^{\left(ix\right)}-e^{\left(-ix\right)}}{2}\\ & =\sinh ix \end{align*}

(2)

\begin{align*} \cos x & =\frac{e^{ix}+e^{-ix}}{2}\\ & =\frac{e^{\left(ix\right)}+e^{\left(-ix\right)}}{2}\\ & =\cosh ix \end{align*}

(3)

\begin{align*} i\tan x & =i\frac{\sin x}{\cos x}\\ & =\frac{\sinh ix}{\cosh ix}\\ & =\tanh ix \end{align*}

(4)

\begin{align*} i\sinh x & =i\sinh\left\{ i(-ix)\right\} \\ & =-\sin(-ix)\\ & =\sin(ix) \end{align*}

(5)

\begin{align*} \cosh x & =\cosh\left\{ i(-ix)\right\} \\ & =\cos(-ix)\\ & =\cos(ix) \end{align*}

(6)

\begin{align*} i\tanh x & =i\frac{\sinh x}{\cosh x}\\ & =i\frac{-i\sin(ix)}{\cos(ix)}\\ & =\tan(ix) \end{align*}