| Complex Number Identities and Formulas | |
|---|---|
| Basic Definitions | |
| imaginary number | $ i=\sqrt{-1} \ $ |
| electrical engineers imaginary number | $ j=\sqrt{-1}\ $ |
| conjugate of a complex number | if $ z=a+jb $, for $ a,b\in {\mathbb R} $, then $ \bar{z}=a-jb $ |
| (more) magnitude of a complex number | $ \| z \| = z \bar{z} $ |
| (more) magnitude of a complex number | $ \| z \| = \sqrt{\left(Re(z)\right)^2+\left(Im(z)\right)^2} $ |
| (more) magnitude of a complex number | $ \| a+jb \| = \sqrt{a^2+b^2} $, for $ a,b\in {\mathbb R} $ |
| (more) magnitude of a complex number | $ \| r e^{j \theta} \| = r $, for $ r,\theta\in {\mathbb R} $ |
| Euler's Formula and Related Equalities | |
| Euler's formula | $ e^{jw_0t}=\cos w_0t+j\sin w_0t \ $ |
| A really cute formula | $ e^{j\pi}=-1 \ $ |
| Cosine function in terms of complex exponentials | $ \cos\theta=\frac{e^{j\theta}+e^{-j\theta}}{2} $ |
| Sine function in terms of complex exponentials | $ \sin\theta=\frac{e^{j\theta}-e^{-j\theta}}{2j} $ |
