Cosine of i/Proof 2

Theorem

$\cos i = \dfrac e 2 + \dfrac 1 {2 e}$

Proof

\(\ds \cos i\)

\(=\)

\(\ds \cosh 1\)

Hyperbolic Cosine in terms of Cosine

\(\ds \)

\(=\)

\(\ds \frac {e^1 + e^{-1} } 2\)

Definition of Hyperbolic Cosine

\(\ds \)

\(=\)

\(\ds \frac e 2 + \frac 1 {2 e}\)

$\blacksquare$