1. Reflection and Rotation Symmetry
Mr. Belanger
Geometry – 9.4

2. Reflection-Symmetric Figures
A figure has symmetry if there is an isometry that maps the figure onto itself. If that isometry is a reflection, then the figure has reflection symmetry.

3. Activity 1:
Lines of symmetry can cut through shapes that have reflection symmetry
Draw in lines of symmetry for each: A C G
none

4. Segment Theorem:
Figures with reflection symmetry have their pre-images and images equal distances from the reflection mirror. 5
5 in
6 in 6 10
10 in

5. Circle Symmetry: Infinite!
How many lines of symmetry does a circle have??
Infinite!

6. Symmetric Figures Theorem:
Any symmetric figure is congruent to its image

7. Rotation Symmetry:
A figure has rotational symmetry if it’s congruent after a rotation of 180 degrees or less (greater than zero).
Find the degrees of roation by dividing 360 by number of points.
360/3 = 120

8. Point Symmetry 360/4 = 90 two rotation make 180
A figure also has point symmetry if it can be rotated 180 degrees.
360/4 = 90 two rotation make 180

9. Examples: Name the type(s) of symmetry each figure has. reflection
Rotation of 120
reflection
Rotation and point
reflection