Chapter 10 - Section 10.3 - Polar Coordinates - Exercises - Page 578: 67

$(0,\theta)$ where $-\infty \lt \theta \lt \infty$

A point in the polar coordinate system is defined as$(r,\theta)$, where $r$ is the distance between the pole and the origin and $\theta$ is the angle. However, when the point is at the origin (0,0) itself then $r=0$. In this case the point can be written as $(0,\theta)$ where $-\infty \lt \theta \lt \infty$ (any angle).