# 12.1: Reflection Symmetry

**At Grade**Created by: CK-12

**Practice**Reflection Symmetry

What if you were asked to consider the presence of symmetry in nature? The starfish, below, is one example of symmetry in nature. Draw in the line(s) of symmetry.

### Reflection Symmetry

A **line of symmetry** is a line that passes through a figure such that it splits the figure into two congruent halves. Many figures have a line of symmetry, but some do not have any lines of symmetry. Figures can also have more than one line of symmetry. A shape has **reflection symmetry** when it has one or more lines of symmetry.

#### Finding Lines of Symmetry

Find all lines of symmetry for the shape below.

This figure has two lines of symmetry.

#### Recognizing Reflection Symmetry

1. Does the figure below have reflection symmetry?

Yes, this figure has reflection symmetry.

2. Does the figure below have reflection symmetry?

Yes, this figure has reflection symmetry.

#### Starfish Problem Revisited

The starfish has 5 lines of symmetry.

### Examples

Find all lines of symmetry for the shapes below.

For each figure, draw lines through the figure so that the lines perfectly cut the figure in half.

#### Example 1

This shape has eight lines of symmetry.

#### Example 2

This shape has no lines of symmetry.

#### Example 3

This shape has one line of symmetry.

### Review

For #1 through #8, determine whether each statement is true or false.

- All right triangles have line symmetry.
- All isosceles triangles have line symmetry.
- Every rectangle has line symmetry.
- Every rectangle has exactly two lines of symmetry.
- Every parallelogram has line symmetry.
- Every square has exactly two lines of symmetry.
- Every regular polygon has three lines of symmetry.
- Every sector of a circle has a line of symmetry.

- What type of shape has an infinite number of lines of symmetry?

Find all lines of symmetry for the letters below.

Determine if the words below have reflection symmetry.

**OHIO****MOW****WOW****KICK****pod**

Trace each figure and then draw in all lines of symmetry.

Determine if the figures below have reflection symmetry. Identify all lines of symmetry.

### Review (Answers)

To view the Review answers, open this PDF file and look for section 12.1.

### Notes/Highlights Having trouble? Report an issue.

Color | Highlighted Text | Notes | |
---|---|---|---|

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Term | Definition |
---|---|

Congruent |
Congruent figures are identical in size, shape and measure. |

Isosceles Triangle |
An isosceles triangle is a triangle in which exactly two sides are the same length. |

Line of Symmetry |
A line of symmetry is a line that can be drawn to divide a figure into equal halves. |

Line Symmetry |
A figure has line symmetry or reflection symmetry when it can be divided into equal halves that match. |

reflection symmetry |
A figure has reflection symmetry if it can be reflected across a line and look exactly the same as it did before the reflection. |

Symmetry |
A figure has symmetry if it can be transformed and still look the same. |

### Image Attributions

Here you'll learn how to determine whether or not a shape has reflection symmetry and how to draw lines of symmetry.

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