$r$ is the distance from the origin to the point in the $xy$-plane, which is given by $r = \sqrt{x^2 + y^2}$. In this case, $x = 1$ and $y = \sqrt{3}$, so $r = \sqrt{1^2 + (\sqrt{3})^2} = 2$.
$\theta$ is the angle between the positive $x$-axis and the line
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