Reflectional Symmetry

Line SymmetryInternal and External

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.

Lines of symmetry can cut through shapes that have reflection symmetry

Draw in lines of symmetry for each:

ACG none

Segment Theorem:Figures with reflection symmetry have their

pre-images and images equal distances from the reflection mirror.

5 in

6 in

10 in

5

6

10

The reflection in this lake also has symmetry, but in this case:•the Line of Symmetry runs left-to-right•it is not perfect symmetry, because the image is changed a little by the lake surface.

Lines of Symmetry

• How many lines of symmetry does the polygon have?

3

Lines of Symmetry

• How many lines of symmetry does the shape have?

2

Lines of Symmetry

• How many lines of symmetry does the shape have?

5

1. If the alphabet were printed in simple block printing, which capital letters would have vertical line symmetry?

2. If the alphabet were printed in simple block printing, which capital letters would have horizontal line symmetry?

3. If the alphabet were printed in simple block printing, which capital letters would have BOTH vertical and horizontal symmetry?

ABCDEFGHIJKLMNOPQRSTUVWXYZ A

HI

M O T U V W X Y

B C D E H I K O X

H I O X

H I O X

4.  Which of the following lettered items possesses line symmetry?  Consider vertical and/or horizontal symmetry.

Circle ALL that apply.a. the letter F

b. an equilateral trianglec. the letter X

d. the word BOOe. a square

f. the word WALLYg. the letter Q