Let be integers. One of the angles of a regular -gon is dissected into angles of equal size by rays. If each of these rays intersects the polygon again at one of its vertices, we say is -cut. Compute the smallest positive integer that is both 3-cut and 4-cut.
Solution
For the sake of simplicity, inscribe the regular polygon in a circle. Note that each interior angle of the regular -gon will subtend of the arcs on the circle. Thus, if we dissect an interior angle into equal angles, then each must be represented by a total of arcs. However, since each of the rays also passes through another vertex of the polygon, that means is an integer and thus our desired criteria is that divides . That means we want the smallest integer such that is divisible by 3 and 4 which is just .
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