Tridecagon
A tridecagon is a polygon with 13 sides. It has an internal angle degree of ~152.308 degrees and a total of 6840 degrees. The area is which is about where is the side length. This cannot be constructed by using a compass and straightedge, but can be constructed using an angle trisector or neusis. But, what if there's is not a side length value given? There is a formula for that too! The side length, where is the radius of the circumcircle that this is being constructed on, of a tridecagon is or . If this was constructed on a unit circle the side length would be . The error of side length being off is 0.0 for up to 15 decimal places, so pretty accurate. If the radius was 1 billion km, then this formula would be off by lass than 1mm. The central angle of a tridecagon is about , which is of by degrees up to 13 decimal places.
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