Solution: A regular 12-sided polygon (dodecagon) has rotational symmetry of order 12. The full set of rotational symmetries consists of rotations by multiples of $ \frac360^\circ12 = 30^\circ $. These rotations are: $ 0^\circ, 30^\circ, 60^\circ, \dots, 330^\circ $. This forms an arithmetic sequence with first term $ 0^\circ $, common difference $ 30^\circ $, and 12 terms. The sum of an arithmetic sequence is given by: - Abu Waleed Tea