## Calculus (3rd Edition)

$$x^2+y^2-2y=0$$
Recall that $x^2+y^2=r^2$ and $r\sin \theta=y$: \begin{align*} r&=2\sin \theta \\ r^2 &=2r\sin \theta \\ x^2+y^2&=2y \end{align*} then $$x^2+y^2-2y=0$$