Third Grade Math: How to Name Line Segments

Learning about Line Segments

How Do Line Segments Work?

In geometry, a line goes on forever in each direction. A line segment, on the other hand, is the space in between two points on a line. Usually, these points are given letter names. In other words, line segments are pieces of lines that are marked with endpoints and letter notations.

Reading Line Segments

Using a ruler, draw a line that's two inches long. Now make one small dot at each end, and one in the middle. Label each dot with a letter. For example, on the left end of the line segment, write 'A.' In the middle, write 'B' and at the right end make a letter 'C.' Now you have created line segments AB, BC, and AC.

You can also write the names of these line segments in reverse order, so the first one would be BA, the second CB, and so on. The order in which you name the points is up to you.

Line Vocabulary

It's important to understand the differences between these related terms in geometry. Being able to tell these things apart will allow you to learn more concepts at a faster pace.

Line

You can probably recognize a line, but you may not know that according to geometry, lines have no beginning and no end. They continue forever, and thus cannot be measured.

Line Segment

This is a piece of a line, with labeled end points on each side. You can measure line segments, and you will often see them in 3rd grade geometry problems.

Ray

A ray is very similar to a line, except that it has a starting point. These starting points are sometimes indicated by arrows. A geometric angle is made of two rays that have the same beginning place.

Parallel Lines

Two lines that are the same distance apart at each point, and therefore never cross, are called parallel lines.

Perpendicular Lines

These are two lines that touch (they may or may not cross) at right angles. Right angles are 90 degrees.

Horizontal Lines

These are lines running east to west.

Vertical Lines

Lines traveling north to south.