Cosine of i/Proof 2
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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 | |||||||||||
\(\ds \) | \(=\) | \(\ds \frac e 2 + \frac 1 {2 e}\) |
$\blacksquare$