1. How many lines of symmetry to these regular polygons have?
Bell Ringer
How many lines of symmetry to these regular polygons have? 5 4 3
Do you see a pattern? 6 8

2. An informal Introduction to Geometry

4. Definitions Topic: Symmetry symmetric line of symmetry Name: Date:
When you can fold a figure in half so that the two halves fit exactly on top of each other, the shape is symmetric.
line of symmetry
The line that contains the fold

5. Examples
The horizontal line through the second T is not a line of symmetry
vertical line of symmetry

6. Symmetry

7. To be a line of symmetry, the shape must have two halves that match exactly.
When you trace a heart onto a piece of folded paper,
and then cut it out, the two half hearts make a whole heart.
The two halves are symmetrical.

8. Which of these flags have a line of symmetry?
United States of America
Canada No
Maryland
England No

9. What about these math symbols?
Do they have symmetry? + -
Yes
Yes - x
Yes
Yes

10. # 2. Describe the lines of symmetry of a circle.
To Do With Your Partner
# 1. Which other letters are symmetric? Which letters are both horizontally symmetric and vertically symmetric?
solution next slide
# 2. Describe the lines of symmetry of a circle.
any line through the center of the circle

11. A B C D E FG H I J K L M N O P Q R S T U V W X Y Z
You can look to see if your name has symmetrical letters in it too!
A B C D E FG
H I J K L M N
O P Q R S T
U V W X Y Z
Infinite number

12. Definitions
Prism
A solid formed by translating a given base shape into the third dimension along a line.
Part of a line that contains two endpoints and all the points between the two endpoints
Line segment

13. Lines in the same plane that do not intersect.
Parallel Lines
Planes in the same space that do not intersect
Parallel Planes
Where do you see parallel lines in the classroom?

14. Homework
p.14 # 5