Course 1

8-11 Line Symmetry8-11 Line Symmetry

Course 1

Warm UpWarm Up

Lesson PresentationLesson Presentation

Problem of the DayProblem of the Day

Course 1

8-11 Line Symmetry

Warm UpTrue 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

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

Learn to identify line symmetry.

Course 1

8-11 Line Symmetry

Vocabulary

line symmetryline of symmetry

Course 1

8-11 Line Symmetry

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.

Course 1

8-11 Line Symmetry

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.

Course 1

8-11 Line Symmetry

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.

Course 1

8-11 Line Symmetry

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.

Course 1

8-11 Line 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.

Course 1

8-11 Line Symmetry

Some figures have more than one line of symmetry.

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

Check It Out: Example 2A

Find all of the lines of symmetry in the regular polygon.

1 line of symmetry

Count the lines of symmetry.

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

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

Course 1

8-11 Line Symmetry

Additional Example 3A: Social Studies Application

Find all of the lines of symmetry in the flag.

Alaska

There are no lines of symmetry.

Course 1

8-11 Line Symmetry

Additional Example 3B: Social Studies Application

Find all of the lines of symmetry in the flag.

Arizona

1 line of symmetry

Course 1

8-11 Line Symmetry

Additional Example 3C: Social Studies Application

Find all of the lines of symmetry in the flag.

Colorado

1 line of symmetry

Course 1

8-11 Line Symmetry

2 lines of symmetry

Additional Example 3D: Social Studies Application

Find all of the lines of symmetry in the flag.

New Mexico

Course 1

8-11 Line Symmetry

Check It Out: Example 3A

2 lines of symmetry

Find all of the lines of symmetry in each design.

Course 1

8-11 Line Symmetry

There are no lines of symmetry.

Check It Out: Example 3B

Find all of the lines of symmetry in each design.

Course 1

8-11 Line Symmetry

1 line of symmetry

Check It Out: Example 3C

Find all of the lines of symmetry in each design.

Course 1

8-11 Line Symmetry

2 lines of symmetry

Check It Out: Example 3D

Find all of the lines of symmetry in each design.

Course 1

8-11 Line Symmetry

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?

3. H 4. R

yes

yes

yes, vertical and horizontal no