Answer
$(-3,-330^\circ), (3,210^\circ),(3,-150^\circ)$.
Work Step by Step
If we have a point $(r,\theta)$, the points $(r,\theta+k360^\circ)$ and $(-r, \theta+180^\circ+l360^\circ)$ with $k,l$ integers will represent the same point. Hence here for $\theta$ to be between $-360^\circ$ and $360^\circ$ we get the following points: $(-3,-330^\circ), (3,210^\circ),(3,-150^\circ)$.
