$\left\{\begin{matrix}P=\frac{R}{\theta }\text{, }&\theta \neq 0\\P\in \mathrm{C}\text{, }&R=0\text{ and }\theta =0\end{matrix}\right.$

$\left\{\begin{matrix}P=\frac{R}{\theta }\text{, }&\theta \neq 0\\P\in \mathrm{R}\text{, }&R=0\text{ and }\theta =0\end{matrix}\right.$

$R=P\theta $