Symmetry

What makes a shape symmetrical?

A 2D shape is symmetrical if a line can be drawn through it and either side of the line is a reflection of the other.

The line is called a line of symmetry.

These shapes all have one vertical line of symmetry.

Some shapes have more than one line of symmetry.

For example, look at these two shapes.

The rectangle has 2 lines of symmetry. One that goes vertically, from top to bottom, and one that goes horizontally, from side to side.

The square has 4 lines of symmetry. These run vertically and horizontally, as well as two other lines of symmetry that run diagonally from corner to corner.

If a shape does not have symmetry it is called asymmetrical.

Activity: What makes shapes symmetrical?

Complete this interactive activity to better understand what makes shapes symmetrical. Then put your knowledge to the test.

What is a line of symmetry?

A line of symmetry is an imaginary line which splits a shape equally in two. Each half must be a mirror image of the other.

If you put a mirror on this line, you would see the whole shape in the reflection.

That’s why a line of symmetry is sometimes called the 'mirror line'.

You could also fold a shape in half and if it fits into itself perfectly with no overlaps, you have found a line of symmetry.

Example 1

Example 2

Example 3