$\left\{\begin{matrix}P=\frac{3q}{r\delta }\text{, }&r\neq 0\text{ and }\delta \neq 0\\P\in \mathrm{R}\text{, }&q=0\text{ and }\delta =0\text{ and }r\neq 0\end{matrix}\right.$

$q=\frac{Pr\delta }{3}$
$r\neq 0$