Lines of symmetry in 2D shapes
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Explainer Video
Summary
Lines of symmetry in 2D shapes
In a nutshell
A 2D shape is symmetrical if you can fold it in half and the two halves are exactly alike. The line separating the identical halves is called the line of symmetry. It is also called the mirror line since either side of the line is the mirror image of the other. Some shapes have more than one line of symmetry.
Lines of symmetry
A line of symmetry is an imaginary line you can draw across a shape, where either side of the line will look identical. This is also called the mirror line because each side is a reflection of the other, like if you held a mirror to it.
Example 1
Is this shape symmetrical?
You can draw a line across the shape and either side will be a mirror image of the other.
Yes, this shape is symmetrical.
Example 2
Is this shape symmetrical?
You cannot draw a line across the shape which would leave either side as a mirror image of the other.
Regular shapes
Regular shapes have all equal sides and equal angles. The lines of symmetry for a regular shape is equal to the number of its sides.
Shape | Number of sides | lines of symmetry |
|---|---|---|
| Equilateral triangle | |  |
| Square | |  |
| Pentagon | |  |
| Hexagon | |  |
Irregular shapes
Irregular shapes have different sized sides and angles. Some also have lines of symmetry.
Shape | lines of symmetry | diagram |
|---|---|---|
| Rectangle | |  |
Rhombus | |  |
| Isosceles triangle | |  |
FAQs - Frequently Asked Questions
What is a regular shape?
Regular shapes have all equal sides and angles.
How do you find a line of symmetry?
A 2D shape is symmetrical if you can fold it in half and the two halves are exactly alike. The line separating the identical halves is called the line of symmetry.
What is a line of symmetry?
A line of symmetry is an imaginary line you can draw across a shape, where either side of the line will look identical.