What is a polygon?
A polygon is a closed flat shape made only of straight sides. A triangle has 3 sides, a square has 4 sides, a pentagon has 5 sides, and a hexagon has 6 sides.
What makes it 'regular'?
A polygon is regular when all its sides are the same length AND all its angles are the same size. If the sides or angles are different, it is an irregular polygon.
- A square is a regular polygon (4 equal sides, 4 equal angles).
- A long, thin rectangle is not regular, because its sides are not all equal.
Key idea
Regular polygon = equal sides + equal angles. Number of sides = number of corners (vertices).
Worked example
A shape has 5 sides that are all the same length and 5 equal angles. How many sides does it have, and what is it called? It has 5 equal sides, so it is a regular pentagon.
Remember
- Count the straight sides to name the polygon.
- Regular means equal sides and equal angles.