Warm Up Problem of the Day Lesson Presentation Lesson Quizzes

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

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

Learn to identify symmetry.

Vocabulary line symmetry line of symmetry rotational 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.

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.

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.

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.

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.

Some figures have more than one line of 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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

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.

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.

Lesson Quizzes Standard Lesson Quiz Lesson Quiz for Student Response Systems

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 4. R yes yes yes, vertical and horizontal; yes no; no

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

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

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

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