What Is A Line Of Symmetry? Symmetrical Shapes Explained For Teachers, Parents and Kids

In this post we will be answering the question “what is a line of symmetry?” and giving you all of the information you need to help your child understand this small, but key math concept! There are a few practice questions for your child to test their skills, so make sure you scroll all the way to the bottom of the blog.

What is a line of symmetry?

A line of symmetry is a line that cuts a shape exactly in half.  

This means that if you were to fold the shape along the line, both halves would match exactly. Equally, if you were to place a mirror along the line, the shape would remain unchanged. 

A square has 4 lines of symmetry, as shown below.

An equilateral triangle has 3 lines of symmetry.

Lines of symmetry in different symmetrical shapes

Your child will learn all about the different shapes and their respective lines of symmetry, but here are some of the most common shapes. 

What will my child learn about lines of symmetry in school?

Children are introduced to symmetry in elementary school, where they should be taught to identify and describe the properties of 2-D shapes, including the number of sides and line symmetry in a vertical line. 

This is then developed when students identify lines of symmetry in 2-D shapes presented in different orientations and complete simple symmetric figures with respect to a specific line of symmetry. 

Students will also be taught to recognize line symmetry in a variety of diagrams, including where the line of symmetry does not dissect the original shape.

Symmetrical shapes (lines of symmetry) practice questions

1)  Here is a shape on a grid. Complete the design so that it is symmetrical about the mirror line. Use a ruler.

2) These two shapes are made from equilateral triangles. Draw one line of symmetry on each shape. Use a ruler.

3) Here is a grid with eight squares shaded in. Shade in two more squares to make a symmetrical pattern.

4) The letter D has a line of symmetry. Check all the other letters that have a line of symmetry.

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The content in this article was originally written by primary school teacher Sophie Bartlett and has since been revised and adapted for US schools by elementary math teacher Christi Kulesza.