## Precalculus (6th Edition) Blitzer

In polar coordinates, the graphs of $r=a\cos \theta$ and $r=a\sin \theta$ are circles.
The graphs of $r=a\sin \theta$ and $r=a\cos \theta$ look like circles of radius $a$ with center at the point $\left( a,0 \right)$ and $\left( a,\frac{\pi }{2} \right)$ on polar coordinates, respectively. The graph of $r=a\sin \theta$ is symmetric with line $\theta =\frac{\pi }{2}$ and the graph of $r=a\cos \theta$ is symmetric with the polar axis.