Line Symmetry Lesson

Focus: Students will determine if different shapes have any lines of symmetry.

Teacher Note: A figure has line symmetry if a line can be drawn through it so that each part is congruent to each other and is a mirror image of the other. If you fold the figure across the line of symmetry, the two parts match exactly. A figure can have one line of symmetry, multiple lines of symmetry or no lines of symmetry. For regular polygons (shapes where the sides are equal), the number of lines of symmetry are equal to the number of sides. When working with shapes, teachers should have examples of both regular and irregular polygons.

Materials:

Block letters, both symmetrical and non-symmetrical, one set per pair

Cut-outs of shapes, both regular and irregular, one set per pair (squares, rectangles, triangles, pentagons, etc.)

Magazines, 2-3 per table group

Introduce:

1. Review the vocabulary term congruent with students. Remind students about the first tetrominoe activity. When making the different shapes, no matter which way the L was slid, rotated, or flipped, the L was always congruent to another L. Students should know that two figures are congruent when they are the same size and same shape, even when slid, rotated, or flipped.

2. Ask students to brainstorm in groups of 3-4 and name things that if folded in half, would be the same or congruent on both sides. Examples would be: butterfly, star, circle, construction paper, and square.

3. Show students pre-made shapes teacher made before class. Fold the shapes to show the line of symmetry. Draw any lines of symmetry on the shapes. Be sure to fold non-symmetrical shapes also so students see non-examples.

Investigate:

1. Students work in groups to look through magazines and around the room for pictures and/or items that have lines of symmetry. Students may glue or draw the items on manila paper. Then, they may draw any lines of symmetry.

2. Discuss items and/or pictures the students have found after about 10-15 minutes of investigating.

3. Students will now work with a partner to sort block letters into symmetrical and non-symmetrical groups. Teachers can cut out letters from a Die-Cut machine or use the attached letters. Students should fold letters and draw any lines of symmetry.

Discussion:

1. Bring the students back together for a discussion. Have students bring their sorted letters and discuss which ones are symmetrical. Do any of the letters have more than one line of symmetry?

2. Assign any of the attached practice pages for individual work or homework. Letter Investigation A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Symmetry Practice 1

1. Draw any lines of symmetry on the figures below.

2. Draw any lines of symmetry on the letters below. Circle the letter that has 2 lines of symmetry.

L H D V

3. Explain how you know if a figure has a line of symmetry. Symmetry Practice 2

1. Draw any lines of symmetry on the figures below.

2. How many lines of symmetry does the figure to the right have?

1 2 3 4

3. Which shape has exactly one line of symmetry?

4. Draw a shape that has two lines of symmetry. Show the lines of symmetry.