Flat shapes
๐ In short
Look around: the door is a rectangle, the clock a circle, the stop sign an octagon and the slice of cheese a triangle. These are flat shapes: we draw them on paper, and they have only length and width. We name them by how many sides and angles they have.
๐คฉ Did you know?
- The angles of any triangle add up to 180 degrees, whatever its shape.
- A honeycomb cell is a hexagon, the shape that holds the most honey with the least wax.
- In most countries the stop sign is a red octagon with 8 sides.
- Every square is a rectangle, but not every rectangle is a square.
๐ Find out more
๐ The triangle
A triangle has 3 sides, 3 angles and 3 corners. Its sides may all be equal (equilateral), or just two of them (isosceles), and it may have a right angle (right-angled). The angles of any triangle add up to 180ยฐ.
๐ Squares and rectangles
Both have 4 sides and 4 right angles. In a square all four sides are equal, while in a rectangle the opposite sides are equal in pairs: a length and a width.
๐ก Polygons
A shape with 5 sides is a pentagon, with 6 sides a hexagon, and with 8 sides an octagon. Honeycomb cells are regular hexagons, and the stop sign on the road is an octagon.
๐ฏ The circle
A circle isn't a polygon: it has no sides or angles. Every point on it is the same distance from its center. We draw it with a compass, and we find it in wheels, plates and clocks.
๐งฎ Worked examples
- Triangle: 3 sidesLike a slice of cheese or a boat's sail.
- Hexagon: 6 sidesLike a honeycomb cell or a nut on a bolt.
- Square: 4 equal sidesLike the squares on a chessboard.
๐ Key words
- Side
- A straight line along one edge of the shape
- Vertex
- The point where two sides meet
- Polygon
- A closed shape whose sides are all straight
๐งช Try it at home
Walk around the house and find 5 rectangular things, 3 round things and one triangular thing. Draw them in a notebook and write the name of each shape and how many sides it has.
๐งฉ Test yourself
1 How many sides does a hexagon have?
2 Which shape has no sides?
3 What do the angles of a triangle add up to?