Line segment

Here you will learn about a line segment, including what it is and how to identify it.

Students will first learn about a line segment as part of geometry in 4 th grade.

What is a line segment?

A line segment is part of a line – it has one end point and the other end goes on forever.

They can be shown on their own.

For example,

They can also be shown within the line.

For example,

Line segments are seen in many common 2D shapes and make up all sides of polygons.

For example,

Each side of a square is made up of line segments – parts of straight lines.

There are also many examples of line segments in real life.

For example,

A side of a ruler is straight and has clear endpoints. It can be represented with a line segment.

In all examples above, line segments can be used to measure. They are measured from one endpoint to the other. Sometimes the measurement is given.

If measuring yourself, just choose one endpoint as a starting point and measure to the other.

For example,

If line segment WZ is 7 \, cm, what are the lengths of the other sides of the square?

Since all the sides of a square are line segments of the same length, they are also 7 \, cm.

What is a line segment?

Common Core State Standards

How does this relate to 4 th grade math?

• 4th Grade – Geometry (4.G.A.1)
  Draw points, lines, line segments, rays, angles (right, acute, obtuse), and perpendicular and parallel lines. Identify these in two-dimensional figures.

How to identify line segments

In order to identify line segments:

1. Look for two endpoints.
2. State the name of the line segment(s) using a pair of letters.

Line segment examples

Example 1: one dimensional

Is the figure a line segment?

1. Look for two endpoints.

The figure is a line, with arrows pointing in each direction going on forever. There are no endpoints shown.

The figure is not a line segment.

Example 2: one dimensional

Name a line segment shown.

Look for two endpoints.

The figure shows a line, with the points G, H and J. Any of these points can be endpoints of a line segment. Let’s look at all the possibilities.

From point G to H:

From point G to J:

From point H to J:

Example 3: line segments in a pentagon

How many line segments are in the pentagon?

Look for two endpoints.

Each vertex can be an endpoint. Let’s look at all the possibilities.

Example 4: lines in a rhombus

How many line segments are in the rhombus?

Look for two endpoints

Each vertex can be an endpoint. Let’s look at all the possibilities.

Example 5: lines in the real world

Find a line segment on the cereal box.

Look for two endpoints.

There are many endpoints. An example is:

The top edge of the box has two endpoints.

State the name of the line segment(s) using a pair of letters.

The edge connected by the points is straight, which means they fall on a line.

The picture below shows all the other line segments:

The line segments are AB, BC, CD, AD, AE, BF, CG, DH, EF, FG, GH, EH.

Example 6: measuring with line segments

Given line segment BE, point R is the midpoint. BR measures 44 \, cm. What is the length of the line segment BE?

State the name of the line segment(s) using a pair of letters.

Since \text { line segment } B R=\text { line segment } R E, \text { line segment } R E=44.

The length of the BR and RE can be added to find the length of line segment BE: 44+44=88.

The length of line segment BE is 88 \, cm.

Teaching tips for line segments

• Give students plenty of opportunities to look for and identify line segments in a variety of places. Worksheets that have a mixture of 2D shapes or real world examples can be useful for this skill, along with physical 2D and 3D objects found in the classroom.

• Encourage students to go beyond just rotely solving practice problems to also creating line segments or requiring them to explain why they classified a figure as a line segment.

Easy mistakes to make

• Confusing lines and line segments
  Line segments have definite endpoints, whereas lines go on forever in opposite directions. This can be confusing, especially since it is impossible to draw a complete line, since they are never ending. This is why it is important to draw lines with arrows on each end and clearly label line segments with two points.

• Thinking that line segments have to be vertical or horizontal
  Line segments, just like lines, can be any orientation. As long as a figure has two endpoints and is part of a line, it is a line segment.
  For example,
  All the figures below are line segments.
  
  

  

• Thinking that line segments have to be a certain length
  As long as a figure has two endpoints and is part of a line, it is a line segment, no matter how short or long.
  For example,
  The dime and the sailboat both have line segments.
  
  

  

  
  

Related lines lessons

• Ray math
• Parallel lines
• Perpendicular lines

The next lessons are

• Angles
• Angles in parallel lines
• 2D shapes
• Quadrilateral
• Triangle

Still stuck?

At Third Space Learning, we specialize in helping teachers and school leaders to provide personalized math support for more of their students through high-quality, online one-on-one math tutoring delivered by subject experts.

Each week, our tutors support thousands of students who are at risk of not meeting their grade-level expectations, and help accelerate their progress and boost their confidence.

Find out how we can help your students achieve success with our math tutoring programs.