An D548: Ordered pair $(r, \theta)$ is a polar representation for $z$ if and only if
| (1) | \begin{equation} r \in [0, \infty) \end{equation} |
| (2) | \begin{equation} \theta \in \mathbb{R} \end{equation} |
| (3) | \begin{equation} z = r e^{i \theta} \end{equation} |