Chapter 11: Parametric Equations and Polar Coordinates - Practice Exercises - Page 688: 34

$r=2\sin \theta$

Consider $x^2+y^2-2y=0$ or, $x^2+(y-1)^2=1$ Here, we get the equation of a circle with center $(0,1)$ and radius $1$ This implies that $r^2-2r \sin \theta=0 \implies r^2=2r \sin \theta$ Hence, $r=2\sin \theta$