Answer
$$\left(3,\:-\sqrt{3}\right)$$
Work Step by Step
Converting the polar coordinates to Cartesian coordinates, we find:
$$x=2\sqrt{3}\cos \left(-\frac{\pi }{6}\right)=3\\ y=2\sqrt{3}\sin \left(-\frac{\pi }{6}\right) =-\sqrt3 \\ \left(3,\:-\sqrt{3}\right)$$