$r^2\cos\theta+2ar\sin^2{\theta\over2}-a^2$ where $a>0$

Question

What does the following equation represent?

$r^2\cos\theta+2ar\sin^2{\theta\over2}-a^2$ where $a>0$

My approach: I factorized the equation and it became $(a+r\cos\theta)(a-r)=0$

I feel that since $(a-r)$ is a factor, $\therefore$ one of the curve is a straight line. But, what is the other curve? Is it a circle? Then, how?