1. Warm Up
Problem of the Day
Lesson Presentation
Lesson Quizzes

2. Warm Up
True or false?
1. In a vertical reflection, the original figure is flipped over a line of symmetry.
2. In a translation, the original figure slides along a straight line and is flipped.
3. In a rotation, a figure is moved around a point.
false
false
true

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.

5. Vocabulary
line symmetry
line of symmetry
rotational symmetry

6. A figure has line symmetry if it can be folded or reflected so that the two parts of the figure match, or are congruent. The line of reflection is called the line of symmetry.

7. Additional Example 1A: Identifying Lines of Symmetry
Determine whether each dashed line appears to be a line of symmetry.
The two parts of the figure appear to match exactly when folded or reflected across the line.
The line appears to be a line of symmetry.

8. Additional Example 1B: Identifying Lines of Symmetry
Determine whether each dashed line appears to be a line of symmetry.
The two parts of the figure do not appear congruent.
The line does not appear to be a line of symmetry.

9. The two parts of the figure do not appear congruent.
Check It Out: Example 1A
Determine whether each dashed line appears to be a line of symmetry.
The two parts of the figure do not appear congruent.
The line does not appear to be a line of symmetry.

10. The line appears to be a line of symmetry.
Check It Out: Example 1B
Determine whether each dashed line appears to be a line of symmetry.
The two parts of the figure appear to match exactly when folded or reflected across the line.
The line appears to be a line of symmetry.

11. Some figures have more than one line of symmetry.

12. Additional Example 2A: Finding Multiple Lines of Symmetry
Find all of the lines of symmetry in the regular polygon.
Trace the figure and cut it out.
Fold the figure in half in different ways.
Count the lines of symmetry.
5 lines of symmetry

13. Additional Example 2B: Finding Multiple Lines of Symmetry
Find all of the lines of symmetry in the regular polygon.
Count the lines of symmetry.
8 lines of symmetry

14. Additional Example 2C: Finding Multiple Lines of Symmetry
Find all of the lines of symmetry in the regular polygon.
Count the lines of symmetry.
4 lines of symmetry

15. Check It Out: Example 2A
Find all of the lines of symmetry in the regular polygon.
Count the lines of symmetry.
1 line of symmetry

16. Check It Out: Example 2B
Find all of the lines of symmetry in the regular polygon.
Count the lines of symmetry.
4 lines of symmetry

17. Check It Out: Example 2C
Find all of the lines of symmetry in the regular polygon.
Count the lines of symmetry.
4 lines of symmetry

18. Additional Example 3A: Social Studies Application
Find all of the lines of symmetry in the flag.
Alaska
There are no lines of symmetry.

19. Additional Example 3B: Social Studies Application
Find all of the lines of symmetry in the flag.
Arizona
1 line of symmetry

20. Additional Example 3C: Social Studies Application
Find all of the lines of symmetry in the flag.
Colorado
1 line of symmetry

21. Additional Example 3D: Social Studies Application
Find all of the lines of symmetry in the flag.
New Mexico
2 lines of symmetry

22. Check It Out: Example 3A
Find all of the lines of symmetry in each design.
2 lines of symmetry

23. Check It Out: Example 3B
Find all of the lines of symmetry in each design.
There are no lines of symmetry.

24. Check It Out: Example 3C
Find all of the lines of symmetry in each design.
1 line of symmetry

25. Check It Out: Example 3D
Find all of the lines of symmetry in each design.
2 lines of symmetry

26. A figure has rotational symmetry if it can be rotated about a point by an angle less than 360° so that it coincides with itself.

27. Additional Example 4A: Identifying Rotational Symmetry
Tell whether each figure has rotational symmetry.
Each time the figure is rotated 90° about its center, the image looks like the original figure.
The figure has rotational symmetry.

28. Additional Example 4B: Identifying Rotational Symmetry
Tell whether each figure has rotational symmetry.
For any rotation less than 360°, the image never looks like the original figure.
The figure does not have rotational symmetry.

29. The figure does not have rotational symmetry.
Check It Out: Example 4A
Tell whether each figure has rotational symmetry.
For any rotation less than 360°, the image never looks like the original figure.
The figure does not have rotational symmetry.

30. The figure has rotational symmetry.
Check It Out: Example 4B
Tell whether each figure has rotational symmetry.
Each time the figure is rotated 180° about its center, the image looks like the original figure.
The figure has rotational symmetry.

31. Lesson Quizzes
Standard Lesson Quiz
Lesson Quiz for Student Response Systems

32. Lesson Quiz
Does the described figure have line symmetry?
1. right isosceles triangle
2. rectangle
Do the following capital letters of the alphabet have symmetry? If so, is the line of symmetry horizontal or vertical? Do the letters have rotational symmetry?
3. H R
yes
yes
yes, vertical and horizontal; yes
no; no

33. Lesson Quiz for Student Response Systems
1. Identify the figure which does not have line symmetry.
A B.
C D.

34. Lesson Quiz for Student Response Systems
2. Identify the figure which has line symmetry.
A B.
C D.

35. Lesson Quiz for Student Response Systems
3. Does the capital letter E of the alphabet have line symmetry? If so, is the line of symmetry horizontal, vertical, or both?
A. yes, horizontal B. yes, vertical
C. yes, both D. no

36. Lesson Quiz for Student Response Systems
4. Does the capital letter J of the alphabet have line symmetry? If so, is the line of symmetry horizontal, vertical, or both?
A. yes, horizontal B. yes, vertical
C. yes, both D. no