Chapter 12 - Parametric Equations, Polar Coordinates, and Conic Sections - 12.3 Polar Coordinates - Preliminary Questions - Page 617: 4

(a)

If $f(\theta )=f(-\theta)$ then the curve $r=f(\theta)$ is symmetric with respect to the x-axis. This is because the negative angle point is the 'mirror' of the positive angle point, reflected over the x-axis. So, the right answer is (a).