1. Everyday Math 6.1 Investigating Line Segments, Rays and Lines
Mrs. Cover
Room 13

2. Objective Students will: Review line segments
Be introduced to rays and lines.

3. Reviewing Line Segments
What is this called?
This is called a
Draw an example of a line segment and label it “line segment”. A B
line segment

4. Reviewing Line Segments
A line segment can be any length, but has two definite endpoints.
What are the endpoints for this line segment?
A and B A B

5. Reviewing Line Segments
A line segement can be named after it’s endpoints.
What could we call this line segment?
Line segment AB
Line segment BA A B

6. Reviewing Line Segments
The name of a line segment can be written with a little bar above the letters.
For example, line segment AB can be written A B AB

7. Reviewing Line Segments
Look around the classroom.
Raise your hand if you can find other objects that resemble line segments.

8. Reviewing Line Segments
Remember:
A line segment can be any length, but must have two definite endpoints.
A line segment is always straight; it is the shortest path between two endpoints.
A line segment can go any direction in space.
Three or more line segments can be used to represent 2 and 3 dimensional figures.

9. Reviewing Line Segments
For example:
-or-

10. Introducing Rays Have you ever heard someone use the word “ray”?
Raise your hand if you know one of the ways you have heard it used.
A ray of light
A ray of sunshine
A person’s name, Ray

11. Introducing Rays
Pretend we extended line segment CD past point D forever.
This is called a C D
ray

12. Introducing Rays
Although it is not possible to see a ray in the real world, because no one can see forever, rays are important to geometry because they help make angles. C D

13. Introducing Rays
It is also not possible to draw a ray that goes on forever, so we show a ray by drawing an arrowhead at one end of the line segment.
Draw an example of a ray and label it “ray”. C D

14. C D Introducing Rays This is called ray CD.
Point C is the endpoint of ray CD.
The first letter always names the endpoint. C D

15. Introducing Rays
The name of a ray can be written with a little arrow above the letters. For example, ray DC can be written: C D DC

16. Real Examples of Rays
What are some examples of rays in the real world?
Sunbeams
Laser beams
Light beams from flashlights
The light starts at a point and goes on forever if nothing gets in its way.

17. Introducing Lines
A line segment has two endpoints, or a start and a finish.
A line, however, has no end.
A line goes on forever in both directions which is represented by arrowheads pointing in both ways. E F

18. E F EF Introducing Lines
The name of a line is written with a double arrow above the letters.
For example, line EF may be written as: E F EF

19. E G F FE Introducing Lines This line can also be named line FE or:
I can also add a point in the middle of my line… E G F FE

20. E G F EG GE GF FG Introducing Lines
Any two points on a line can be used to name the line. For example, this line could be named either: E G F EG GE GF FG

21. E G F Introducing Lines Why does a line not have endpoints?
Because a line goes on forever in both directions with no starting or stopping points. E G F

22. Real Examples of Lines
Numbers on a number line go on forever in both positive and negative directions.
The arrows on the end of number lines mean the same thing as the arrows on representations of lines.

23. Great job 3rd graders! Remember:
Letter labels for rays can only be written in one order: the letter for the starting point is written first!
Letter labels for line segments and lines may be written in either order.
When drawing line segments, make sure your line does not go beyond your endpoints!

24. Great job 3rd graders!
Please take out your math journals and turn to page 128 for some practice with line segments, rays, and lines.