Answer
To test the symmetry with respect to the polar axis, replace $\theta \,\text{with}\,-\theta $.
If an equivalent equation results, then the graph is symmetric with respect to the polar axis.
Work Step by Step
For example:
We will replace $\theta \,\text{with}\,-\theta $ in the polar equation $r=1-2\cos \theta $ to perform the test for the polar axis,
$\begin{align}
& r=1-2\cos \left( -\theta \right) \\
& r=1-2\cos \theta \\
\end{align}$
The resultant equation remains the same.
Thus, the equation is symmetric with respect to the polar axis.
