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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
existed).

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

http://mathforum.org/dr.math/faq/formulas/faq.sphere.html#lune

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
http://mathforum.org/dr.math/
```
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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