Transcript Course 3 Chapter 5 Lesson 8

Symmetry
5.8
Pre-Algebra
Warm Up
Identify each as a translation, rotation,
reflection, or none of these.
B.
A.
rotation
reflection
C.
D.
none of the these
translation
Learn to identify symmetry in figures.
Vocabulary
line symmetry
line of symmetry
rotational symmetry
Nature provides beautiful examples of symmetry, such as
the wings of a butterfly or petals of a flower. Symmetric
objects have parts that are congruent.
VOCAB: A figure has line symmetry if you can
draw a line through it so the the two sides are
mirror images of each other. The line is called
line of symmetry.
Helpful Hint
If you fold a figure on the line of symmetry, the
halves match exactly.
Example: Drawing Figures With Line
Symmetry
Complete the figure. The dashed line is
the line of symmetry.
A.
Example: Drawing Figures With Line
Symmetry Continued
Complete the figure. The dashed line is
the line of symmetry.
B.
Try This
Complete the figure. The dashed line is
the line of symmetry.
A.
Try This
Complete the figure. The dashed line is
the line of symmetry.
B.
VOCAB: A figure has rotational symmetry if
you can rotate the figure around some point so
that it coincides with itself. The point is the
center of rotation, and the amount of rotation
must be less than one full turn or 360°. To find
the amount of degrees you can turn the figure
so that it looks the same, divide 360 by the
number of “folds”.
6-fold rotational symmetry
8-fold rotational symmetry
The figure coincides with itself every
60° (360/6)
The figure coincides with itself every
45° (360/8)
Example: Drawing Figures With
Rotational Symmetry
Complete the figure. The point is the
center of rotation.
A. 2-fold
The figure coincides
with itself every 180°
Example: Drawing Figures With
Rotational Symmetry Continued
Complete the figure. The point is the
center of rotation.
B. 5-fold
The figure coincides
with itself every 72°
Try This
Complete the figure. The point is the
center of rotation.
A. 8-fold
The figure coincides
with itself every 45°
Try This
Complete the figure. The point is the
center of rotation.
B. 10-fold
The figure coincides
with itself every 36°
Lesson Quiz: Part 1
Does the figure described have symmetry?
1. a regular hexagon
yes
2. the letter F
no
3. the letter M
yes
Lesson Quiz Part 2
4. Complete the figure. The dashed line is the
line of symmetry.