Euler's formula


Euler's formula is an equation in complex analysis that allows one to convert between trigonometric functions and complex exponentials. It states

eiθ=sinθ+icosθe^{i\theta}=\sin \theta+i\cos \theta

When θ=π\theta=\pi, it takes on a form known as Euler's identity:

eiπ=1e^{i\pi}=-1

This formula can be used to rewrite the sine and cosine as complex functions:

sinθ=eiθeiθ2i,cosθ=eiθ+eiθ2\sin \theta=\frac{e^{i\theta}-e^{-i\theta}}{2i},\qquad \cos \theta=\frac{e^{i\theta}+e^{-i\theta}}{2}