## Oriented line - axis

A straight *r* is oriented when a direction of travel is *positive*, being indicated by an arrow.

## Targeted Segment

A oriented segment is determined by an ordered pair of points, the first called *source* of the segment, the second called *far end*.

## Null segment

A null segment is one whose end coincides with the origin.

## Opposite Segments

If **AB** is an oriented segment, the oriented segment **BA** is opposite of **AB**.

## Measurement of a segment

Once a unit of length is set, each oriented segment can be associated with a real, nonnegative number, which is the measure of the segment with respect to that unit. The measure of the oriented segment is its *length* or yours *module*. The segment length **AB** is indicated by .

So the length of the segment **AB** shown in the figure below is 5 units in length:

= 5 u.c.

*Comments*:

Null segments are zero length.

= .