Reflection and Rotation Symmetry

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 6 in 10 10 in

5. Circle Symmetry: 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 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 Rotation and point reflection