Chapter 8 - Complex Numbers, Polar Equations, and Parametric Equations - Section 8.5 Polar Equations and Graphs - 8.5 Exercises - Page 389: 43

graph A

$r = cos~2\theta$ When $\theta = 0^{\circ}$, then $r = cos~2\theta = 1$ When $\theta = 90^{\circ}$, then $r = cos~2\theta = -1$ When $\theta = 180^{\circ}$, then $r = cos~2\theta = 1$ When $\theta = 270^{\circ}$, then $r = cos~2\theta = -1$ We can see that this matches up with graph A.