1. 5-8 Symmetry Warm Up Problem of the Day Lesson Presentation
Pre-Algebra

2. 5-8 Symmetry Warm Up 1.  360 2.  360 3.  360 4.  360 5.  360 1 1
Pre-Algebra
5-8
Symmetry
Warm Up
1.   360
3.   360
5.  360 1 4 1 2 90
180 1 8 3 5 45
216 2 3
240

3. Problem of the Day
Name four plane figures that can be rotated 180° around a center point and look the same after the rotation as they did before.
Possible answer:
rectangle, square, parallelogram, regular hexagon.

4. Learn to identify symmetry in figures.

5. Vocabulary
line symmetry
line of symmetry
rotational symmetry

6. 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.
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.

7. If you fold a figure on the line of symmetry, the halves match exactly.
Helpful Hint

8. Additional Example 1A: Drawing Figures With Line Symmetry
Complete the figure. The dashed line is the line of symmetry. A.

9. Additional Example 1B: Drawing Figures With Line Symmetry Continued
Complete the figure. The dashed line is the line of symmetry. B.

10. Try This: Example 1A
Complete the figure. The dashed line is the line of symmetry. A.

11. Try This: Example 1B
Complete the figure. The dashed line is the line of symmetry. B.

12. 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°.
8-fold rotational symmetry
6-fold rotational symmetry

13. Additional Example 2A: 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°

14. Additional Example 2B: 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°

15. A. 8-fold Try This: Example 2A
Complete the figure. The point is the center of rotation.
A. 8-fold
The figure coincides with itself every 45°

16. B. 10-fold Try This: Example 2B
Complete the figure. The point is the center of rotation.
B. 10-fold
The figure coincides with itself every 36°

17. 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

18. Lesson Quiz Part 2
4. Complete the figure. The dashed line is the line of symmetry.