Geometry
2D shapes and symmetry
A 2D shape is flat. In this section you will name 2D shapes by counting their sides, and learn about symmetry and lines of symmetry.
Naming 2D shapes
You can name a flat shape by counting its straight sides. ā¢ triangle: 3 sides ā¢ square and rectangle: 4 sides ā¢ pentagon: 5 sides ā¢ hexagon: 6 sides ā¢ octagon: 8 sides A circle is round with no straight sides. A shape with straight sides is called a polygon.
What is symmetry?
Something is symmetrical when it is the same on both sides. One half is a mirror image of the other half.
Lines of symmetry
A line of symmetry is a line you can fold along to make both halves the same. It can be vertical (up and down the middle) or horizontal (across the middle).
Worked examples
Naming a shape by its sides
- Look at the shape and count the straight sides.
- There are 5 sides.
Answer: A flat shape with 5 sides is a pentagon.
Finding a line of symmetry
- Imagine folding the shape in half.
- If both halves match exactly, the fold is a line of symmetry.
Answer: The fold line that makes both halves match is a line of symmetry.
Counting sides
- Look at an octagon.
- Count each straight side carefully.
Answer: An octagon has 8 sides.
Where you see this in real life
- A road sign can be an octagon.
- A honeycomb is made of hexagons.
- A butterfly's wings are symmetrical.
Key words
- 2D shape
- A flat shape, like one drawn on paper.
- Polygon
- A flat shape with straight sides.
- Symmetry
- When a shape is the same on both sides.
- Line of symmetry
- A line you can fold along so both halves match.
- Pentagon
- A shape with 5 sides. A hexagon has 6 and an octagon has 8.