Questions on polar coordinates, a coordinate system where points are represented by their distance from the origin ($r$) and the angle the line joining the point and the origin makes with the positive horizontal axis ($\theta$).

Polar coordinates are a two-dimensional coordinate system. They consist of the radial and angular coordinate, where each point on the plane is recognised by a distance and angle from a reference point.

It is determined by the following diffeomorphism $$ \boldsymbol\varphi \begin{bmatrix}\rho\\\phi \end{bmatrix} = \begin{bmatrix}\rho\cos\phi \\ \rho\sin\phi \end{bmatrix}: [0,\infty[ \times ]-\pi,\pi[ \to \mathbb{R}^2 \setminus \biggl\{\begin{bmatrix} 0\\0\end{bmatrix}\biggr\} $$ $0$ is called the pole of the polar coordinates.