Warm Up1. Give the coordinates of triangle ABC with

vertices (7, 2), (1, 2), (4, –5) reflected across the y-axis.

2. Give the coordinates of triangle ABC

translated 3 units left and 2 units down.

Course 2

7-11 Symmetry

Learn to identify symmetry in figures.

Course 2

7-11 Symmetry

Vocabulary

line symmetryline of symmetryasymmetryrotational symmetrycenter of rotation

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Course 2

7-11 Symmetry

When you can draw a line through a plane figure so that the two halves are mirror images of each other, the figure has line symmetry, or is symmetrical. The line along which the figure is divided is called the line of symmetry.

When a figure is not symmetrical then it has asymmetry, or is asymmetrical

Course 2

7-11 Symmetry

Decide whether each of the figures has line symmetry. If it does, draw all the lines of symmetry.

Additional Example 1: Identifying Line Symmetry

A. B.

no line of symmetry 1 line of symmetry

Course 2

7-11 Symmetry

Try This: Example 1A & 1B

Decide whether each figure has line symmetry. If it does, draw all lines of symmetry.

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A. B.

1 line of symmetry no line of symmetry

Course 2

7-11 Symmetry

Find all the lines of symmetry in each figure.

Additional Example 2A & 2B: Finding Lines of Symmetry

A.There are two linesof symmetry.

B. There are no linesof symmetry.

Course 2

7-11 Symmetry

Try This: Example 2A & 2B

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Find all the lines of symmetry in each figure.

B. There is 1 lineof symmetry.

A. There are no linesof symmetry.

Course 2

7-11 Symmetry

A figure has rotational symmetry if, when it is rotated less than 360° around a central point, it coincides with itself. The central point is called the center of rotation.

Course 2

7-11 Symmetry

Additional Example 3A: Identifying Rotational Symmetry

Tell how many times each figure will show rotational symmetry within one full rotation.

A. Draw lines from the centerof the figure out throughidentical places in the figure.

Count the number of linesdrawn.

The figure will show rotational symmetry 5 times within a 360° rotation.

Course 2

7-11 Symmetry

Tell how many times each figure will show rotational symmetry with one full rotation.

Additional Example 3B: Identifying Rotational Symmetry

Draw lines from the center of the figure out throughidentical places in the figure.

Count the number of lines drawn.

The figure will show rotational symmetry 4 times within a 360° rotation.

B.

Course 2

7-11 Symmetry

Try This: Example 3A

Tell how many times each figure will show rotational symmetry within one full rotation.

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A.Draw lines from the center of the figure out through identical places in the figure.

Count the number of lines drawn.

The figure will show rotational symmetry 4 times within a 360° rotation.

Course 2

7-11 Symmetry

Try This: Example 3B

Insert Lesson Title Here

Tell how many times each figure will show rotational symmetry within one full rotation.

B. Draw lines from the center of the figure out throughidentical places in the figure.

Count the number of lines drawn.

The figure will show rotational symmetry 4 times within a 360° rotation.

Course 2

7-11 Symmetry

Lesson Quiz

Does the figure described have symmetry?

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1. a regular hexagon with a line drawn through the middle and two vertices2. a square with a diagonal line drawn in3. a heart with a horizontal line drawn through the middle4. Tell how many times the figure will have rotational symmetry with one full rotation.

yesyes

no

6

Course 2

7-11 Symmetry

Assignment

• Page 398 – 399– # 1 – 23, 27 - 34