Ray, Line Segment, Line

Date: 08/23/97 at 15:41:13
From: Naomi Johnson
Subject: Geometry

I need to know what ray, line segment, and line are.

Date: 08/26/97 at 12:45:54
From: Doctor Ken
Subject: Re: Geometry

Hi Naomi -

In Geometry, you can think of a line as just like a normal straight 
line, except that it goes on forever in both directions.  It's also 
_perfectly_ straight, and it's not thick. 

Mathematicians say that their lines have "zero thickness," which is 
pretty hard to imagine.  When we draw lines on paper, they always have 
at least a little bit of width. But when we study lines in Geometry, 
we think of them as having no width at all.

Here's how a lot of people draw lines on paper.  The arrows at the end 
mean that the line continues forever in that direction:

     /____________________________________________________\
     \                                                    /


Rays and line segments are a lot like lines.  A ray is like a line, 
except that it only goes on forever in one direction. So it starts at 
one point, and goes off forever in some direction. You can think of 
the light coming from the sun as an example of a ray: the starting 
point is at the sun, and the light goes off forever away from the sun.  
Here's how people draw rays:

      ____________________________________________________\
                                                          /

A line segment is a little chunk of a line.  It starts at one point, 
goes for a while, and ends at another point.  People draw them like 
this:

      ____________________________________________________

                                                              
Sometimes people like to put little dots connected to the ends of rays 
and segments, like this:

      .____________________________________________________\
                                                           /

      .____________________________________________________.
                                                              

I hope you enjoy learning about Geometry!  Good luck with the rest of 
your math.

-Doctor Ken,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/