## Precalculus (6th Edition) Blitzer

To convert a complex number in rectangular form, $z=a+bi$, to polar form, $z=r\left( \cos \theta +i\sin \theta \right)$, we use the relationships $r=$ $\sqrt{{{a}^{2}}+{{b}^{2}}}$ and $\tan \theta =$ $\frac{b}{a}$, noting the quadrant in which the graph of $z$ lies.