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One- and Two-sided Polygons

Date: 12/07/1999 at 15:56:45
From: Sue
Subject: Polygons

Dr. Math:

You said that there are such things as monogons and digons - one-sided 
and two-sided polygons. What are they? None of my math teachers has 
heard of them. Please write back with a little diagram of each.

Thank you.

Date: 12/07/1999 at 16:13:32
From: Doctor Rob
Subject: Re: Polygons

Thanks for writing to Ask Dr. Math, Sue.

Since there is no such thing, it would be really hard to draw a 
diagram of either. The names are constructed by analogy with names of 
figures with more sides. Mono- means one, Di- means two, and Octa- 
means 8. Thus Octagon for an 8-sided figure would correspond to Digon 
for a 2-sided one (if it existed) or Monogon for a 1-sided one (if it 

Actually, on the surface of a sphere, you *can* have such figures: a 
monogon is a hemisphere, and a digon is a spherical lune (see


for pictures). Of course you have to replace straight lines with great 
circles on the sphere for the sides, but that is standard practice in 
spherical geometry and trigonometry.

- Doctor Rob, The Math Forum
Associated Topics:
High School Definitions
High School Geometry
High School Triangles and Other Polygons
High School Trigonometry
Middle School Definitions
Middle School Geometry
Middle School Triangles and Other Polygons

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