Lines, Rays and Segments

In geometry, a line is straight and goes on forever.  To indicate that a line goes on forever, we usually draw lines with arrows on both ends, like this:

 

Lines are sometimes labeled by indicating two points on them and placing a double arrow over the names of the points (which are capital letters).  For example, the line that goes through points A and B might be labeled as :

 

If we choose a point on a given line this divides the line into two pieces or "halves."  Each half is called a ray.  More precisely, a ray consists of a point on a line, called its vertex, and all points on one side (or half) of that line.  A ray goes on forever, but only in one direction.  We draw rays with an arrow on one side only, like this:

Rays are labeled by specifying the vertex and some other point on it, and placing an arrow over these letters.  Ray  would look like this: 

If we choose two distinct points on a line, the line is split into three pieces.  The piece that consists of those two points and all the points between them is called a segment.  Segments do not go on forever, so we do not put arrows on their ends.  The endpoints of segments are called its vertices, and we label segments by specifying the endpoints and placing a line without arrows over these letters.  Segment  would look like this: 

 

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