Line Segments & Rays: Definition & Measurement

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  • 0:07 What Is a Ray?
  • 1:02 What Is a Line Segment?
  • 1:36 Measuring Distance
  • 2:20 Adding Them Up
  • 3:11 Lesson Summary
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Lesson Transcript
Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Watch this video lesson to learn the difference between a line segment and a ray. You will also learn how to measure and add line segments. Learn why you can't measure or add a ray.

What is a Ray?

A ray is a line that starts at one point and continues forever in one direction. So if we have a starting point labeled A, by placing a second point B somewhere else, we will be telling the ray in which direction to go. We would draw a line connecting points A and B, but we would continue the line past B towards infinity.

For rays, we don't need to measure or add them together. We just label them with the two points, starting with the start point, and then we put a little arrow on top to tell us in which direction the ray is going. So for our ray with a starting point of A and going towards point B, we would identify it like this:


What is a Line Segment?

A line segment is a line with a starting point and an end point. Unlike a ray, a line segment has a finite stop. We label line segments similar to rays, except the points will be our start and stop point and the little arrow on top changes to a short line like this:

line segment

If we had points A and B, a line segment would show just a line connecting points A and B. It would not go beyond these points.

Measuring Distance

Because line segments have a start and end point, we can measure their distance as well as add them. To measure the distance of a line segment, you can simply take your ruler and measure the actual line segment.

Some problems show a line segment on top of a number line. In this case, you would look to see where the line segment begins and where it ends. Then you would subtract the lower number from the higher number to get your distance. For example, if your line segment begins at 2 and ends at 5, then the distance of this line segment is 5 - 2 = 3.

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