Answer
In general, the completed statements in parts (a)-(e) mean that the graphs of polar equations of the form $r = a \pm b~cos~\theta$ (where $a$ may be 0) are symmetric with respect to polar axis.
Work Step by Step
Note that $cos~(-\theta) = cos~\theta$
According to part (a), the graph of $r = f(\theta)$ is symmetric with respect to the polar axis if substitution of $-\theta$ for $\theta$ leads to an equivalent equation.
In general, the completed statements in parts (a)-(e) mean that the graphs of polar equations of the form $r = a \pm b~cos~\theta$ (where $a$ may be 0) are symmetric with respect to polar axis.
