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Geometry Difficulty 3.3 AMC 10/12 Find the answer

For how many values of nn will an nn-sided regular polygon have interior angles with integral measures?

Pick one

Solution

Start with the facts that all polygons have their exterior angles sum to 360 and the exterior and interior angles make a linear pair of angles. So our goal is to find the number of divisors of 360 to make both the interior and exterior angles integers. The prime factorization of 360 is 233252^3 * 3^2 * 5. That means the number of divisors is 4*3*2 = 24. But we're not done yet. We cannot have a 1 or 2 sided polygon so we subtract off two bringing us to our final answer of 22 D\fbox{D}.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.