Precalculus (6th Edition) Blitzer

The rectangular equation is, $x=0$
Using, $\tan \theta =\frac{y}{x}$, we will convert the given polar equation to the rectangular equation. Therefore, \begin{align} & \tan \frac{\pi }{2}=\frac{y}{x} \\ & x=\frac{y}{\tan \frac{\pi }{2}} \\ & =\frac{y}{\infty } \\ & =0 \end{align}