Associated Topics || Dr. Math Home || Search Dr. Math

### How to Name a Polygon by Vertices

```Date: 06/30/2004 at 19:26:23
From: Claudia
Subject: variable naming convention

Is there a specific convention for naming the vertices of polygons?
For example, picture a triangle with vertices at R (0, 0), S (0, 3),
and T (4, 0).  Would you call this triangle RST or RTS?

In other words, is the figure named by going clockwise or counter-
clockwise?  How do you determine the first vertex named?  Are there
ever exceptions?

```

```
Date: 06/30/2004 at 23:06:50
From: Doctor Peterson
Subject: Re: variable naming convention

Hi, Claudia.

A triangle can be named in any order at all; a polygon in general can
be named by starting at any point and going either clockwise or
counterclockwise.

There is good reason for this.  In many cases we don't care about the
direction or the starting point; it makes no difference in most
theorems.  Usually we don't even know the direction of the points;
that is not one of the facts given in the statement of the theorem.
And perhaps most important, we need to be able to say in a figure
like this

A
/|\
/ | \
/  |  \
/   |   \
/    |    \
C-----B-----D

that triangles ABC and ABD are congruent; but if we had to name
triangles in a certain order, then one of these two names would be
illegal, since if one is clockwise then the other has to be
counterclockwise!

So don't worry about consistency.  In fact, if you are teaching, you
should deliberately name triangles in different orders, to get
students used to the fact that naming does not imply anything about
orientation.

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Triangles and Other Polygons

Search the Dr. Math Library:

 Find items containing (put spaces between keywords):   Click only once for faster results: [ Choose "whole words" when searching for a word like age.] all keywords, in any order at least one, that exact phrase parts of words whole words

Submit your own question to Dr. Math
Math Forum Home || Math Library || Quick Reference || Math Forum Search