Polygons
Word Polygon is derived from the Greek “poly” meaning many and “gonia” meaning angles.
Note: The lines making the polygon , cannot intersect each other.
Figures shown below are NOT polygons even though first two are made up of finite straight lines.
Figure shown below are polygons
Polygons can have any number of sides and they are named according to the number of their sides or angles.
Names of polygons usually comprise of a prefix and a suffix. Prefix is mostly derived from Greek and mostly the suffix is –“gon”
So a five sided figure would be called Penta + gon = Pentagon.
Sometimes, suffix “gon” is replaced with “gram”.
For example, penta+gram = Pentagram
In Hindi, names have prefix “kod” (कोड/कोण) meaning angle or “bhuj(भुज) meaning side or arm.
Number of sides | Popular English name | Hindi names | डेवनागरी में बहुभुजों के नाम |
3 | Triangle | Trikon | त्रिकोड |
4 | Tetragon Quadrilateral | Chaturbhuj | चतुर्भुज |
5 | Pentagon Pentagram | Panchbhuj | पंचभुज |
6 | Hexagon | Shatbhuj | षट्भुज |
7 | Heptagon
Septagon | Saptkodak Saptabhuj | सातकोणक सप्तभुज |
8 | Octagon | Ashtabhuj Ashtakod | अष्टकोण अष्टभुज |
9 | Nonagon Enneagon | Navbhuj | नवभुज |
10 | Decagon | Dasbhuj | दसभुज |
11 | Hendecagon Undecagon | Ekdashbhuj | एकदशभुज |
12 | Dodecagon | Barahkod Dwadashbhuj | बारहकोना द्वादशभुज |
13 | Tridecagon | Tehrah Paksiya Bahubhuj | तेरह-पक्षीय बहुभुज |
14 | Tetradecagon | Dvisamalanabaksh | द्विसमलंबाक्ष |
15 | Pentadecagon |
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* : Uni or Un are Roman prefixes, hence the term Hendecagon is preferred as both prefix and suffix are Greek.
Various Greek, Latin and Roman suffixes are used to name polygons of larger number of sides but these are not commonly used. Hence, a polygon with many sides may also be referred as n-gon, for example a 22 sided figure can be called twenty two-gon.
Higher order names with Greek , Roman and Latin prefixes are used more for academic interest. Similar is the case with Hindi names of polygons.
Kinds of Polygons
Polygons are classified
as
1. Regular polygons have all sides equal,
and hence, all interior and exterior angles are also equal.
2. Irregular polygons all sides , and hence, all angles, are not necessarily equal.
3. Convex polygons have all interior angles are less than 180.
4. Concave Polygons in which one or more interior angles are reflex angles (more than 180).
Another
method to check if a polygon is convex or concave :
 |
| Concave polygon |
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| Convex polygon |
