Other Definitions
polygon (dict)
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PolygonA polygon (from the Greek poly, for "many", and gonos, for "angle") is a closed planar path composed of a finite number of sequential line segments. The straight line segments that make up the polygon are called its sides or edges and the points where the sides meet are the polygon's vertices. If a polygon is simple, then its sides (and vertices) constitute the boundary of a polygonal region, and the term polygon sometimes also describes the interior of the polygonal region (the open area that this path encloses) or the union of both the region and its boundary. Names and types Polygons are named according to the number of sides, combining a Greek root with the suffix -gon, e.g. pentagon, dodecagon. The triangle and quadrilateral are exceptions. For larger numbers, mathematicians write the numeral itself, eg 17-gon. A variable can even be used, usually n-gon. This is useful if the number of sides is used in a formula. Naming polygons To construct the name of a polygon with more than 20 and less than 100 sides, combine the prefixes as follows | colspan="2" rowspan="2" | Tens | and | colspan="2" | Ones | final prefix | | rowspan="9" | -kai- | 1 | hena- | rowspan=9 | -gon | | 20 | icosi- | 2 | -di- | | 30 | triaconta- | 3 | -tri- | | 40 | tetraconta- | 4 | -tetra- | | 50 | pentaconta- | 5 | -penta- | | 60 | hexaconta- | 6 | -hexa- | | 70 | heptaconta- | 7 | -hepta- | | 80 | octaconta- | 8 | -octa- | | 90 | enneaconta- | 9 | -ennea- | That is, a 42-sided figure would be named as follows: | Tens | and | Ones | final prefix | full polygon name | | tetraconta- | -kai- | -di- | -gon | tetracontakaidigon | and a 50-sided figure | Tens | and | Ones | final prefix | full polygon name | | pentaconta- | colspan="2"| | -gon | pentacontagon | But beyond nonagons and decagons, professional mathematicians prefer the aforementioned numeral notation (for example, MathWorld has articles on 17-gons and 257-gons).
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