An octadecagon is a polygon with 18 sides and 18 vertices. Another name for an octadecagon is octakaidecagon. ==Construction== A regular octadecagon cannot be constructed using a compass and straightedge. == Uses == A regular triangle, enneagon, and octadecagon can completely surround a point in the plane, one of 17 different combinations of regul...
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http://en.wikipedia.org/wiki/Octadecagon
An 18 sided polygon. See also: Polygon.
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https://www.encyclo.co.uk/local/20687
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