1n sides means an n-gon
A polygon is a shape surrounded by straight line segments. Its name simply follows the number of sides. 5 sides is a pentagon, 6 sides a hexagon, and so on. And the number of sides always matches the number of corners.
2A regular polygon has equal sides and equal angles
A polygon where every side is the same length and every angle is the same size is called a regular polygon — like an equilateral triangle or a square. The shape you build on the activity page by changing the number of sides is exactly this kind of regular polygon.
3Convex and concave are a whole different measure
Regardless of how many sides it has, a polygon can also be sorted into convex and concave. If there's no spot that caves inward in any direction, it's a convex polygon; if even one spot caves inward like an arrow, it's a concave polygon.
Every regular polygon is convex. But a concave polygon can never be regular.
Pick any two points on the polygon and draw a line between them. If that line ever steps outside the shape, it's concave; if it always stays inside, it's convex.
4Try playing like this
- Increase the number of sides one at a time. Watch how a regular polygon's shape gets closer and closer to a circle as the sides increase.
- Try the name-that-shape quiz. Practice naming a shape the instant you see it, without having to count the sides.
- Practice telling convex from concave. Decide by imagining whether a line between two points would ever step outside the shape.