Cosine Exponential Formulation

Theorem
For any complex number $x$:
 * $\cos x = \dfrac {e^{i x} + e^{-i x} } 2$

where $\cos x$ is the cosine and $i^2 = -1$.

Also presented as
This result can also be presented as:
 * $\cos x = \dfrac 1 2 \left({e^{-i x} + e^{i x} }\right)$

Also see

 * Sine Exponential Formulation
 * Tangent Exponential Formulation
 * Cotangent Exponential Formulation
 * Secant Exponential Formulation
 * Cosecant Exponential Formulation


 * Arccosine Logarithmic Formulation