Triangles in n-gons and more...

Geometry Level pending

Three vertices of a regular n-gon are connected to form a triangle, and the angles are in the ratio 2 : 1006 : 1007 2:1006:1007 . What's the minimum number of sides for this regular n-gon?


The answer is 2015.

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1 solution

Dylan Pentland
Mar 15, 2015

Because we're considering a regular n-gon, we can inscribe it in a circle. We can denote the arc length between two neighboring vertices of the n-gon as θ \theta degrees. Call the triangle A B C ABC . By power of the point, we get that A B C = a θ 2 \measuredangle ABC=\frac { a\theta}{ 2 } where a a is the number of sides of the n-gon contained by arc B C BC . Thus, we find that the angles are in the same ratio as the number of sides of the n-gon contained by each arc of two vertices of the triangle. The ratio given cannot be simplified, so the answer is just 2015 2015 . (This is just letting one arc contain two sides, another 1006 1006 and another 1007 1007 .)

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