Answer
$\theta=\frac{\pi}{6}$
Work Step by Step
1. Given the line passing $(0,0)$ and slope $m=tan30^\circ=\frac{\sqrt 3}{3}$, thus we have $y=\frac{\sqrt 3}{3}x$ in rectangular coordinates.
2. We have $r\ sin\theta=\frac{\sqrt 3}{3}r\ cos\theta$ or $tan\theta=\frac{\sqrt 3}{3}$ or $\theta=\frac{\pi}{6}$
