Euler's Formula/Proof

Theorem

 * $e^{i \theta} = \cos \theta + i \sin \theta$

where $e^{i \theta}$ is the complex exponential function, $\cos$ is cosine, $\sin$ is sine, and $i$ is the imaginary unit.

Proof
As Sine Function is Absolutely Convergent and Cosine Function is Absolutely Convergent, we have: