# Euler's formula

Euler’s formula is the most important tool in AC analysis. It is why electrical engineers need to understand complex numbers. It relates the complex exponential $e^{\pm j\text{something}}$ to the cosine and sine functions.

Sal derives Euler’s formula here using McLaurin expansions of $e^{ix}, \sin x,$ and $\cos x$.

Created by Willy McAllister.