Sides and vertices

Every polygon has two kinds of parts:

• Sides — straight line segments that form the edge of the shape.
• Vertices — the corners of the shape. Where two sides meet, that is a vertex.

A handy rule: as many sides, as many vertices. Always.

Count them

Triangle — 3 sides, 3 vertices.

The word "triangle" has "tri" (three) inside it — easy to remember.

Square and rectangle — 4 sides, 4 vertices.

A square has all sides the same length. A rectangle has two longer and two shorter.

Pentagon — 5 sides, 5 vertices. Picture a child's drawing of a little house: a square with a triangular roof. Hexagon — 6 sides, 6 vertices. That is the shape of a honeycomb cell or the road sign "Stop".

Trick: count with your finger

A method that always works:

1. Put your finger on one vertex.
2. Tap it. Say "1".
3. Slide your finger along a side to the next vertex.
4. Tap it. Say "2".

Carry on until you have gone around the whole shape and ended up back at the start. The last number you said is the number of vertices (and at the same time the number of sides).

How do you spot a polygon

A polygon is a closed shape made only from straight lines. So:

• Circle is not a polygon — it has one curved side and no vertices.
• Half-circle is also not — it has a curved side.
• Star — it has points, and if its sides are straight, it is a polygon (10 sides, 10 vertices for a five-pointed star).

Summary

• Side = a straight line on the edge of the shape.
• Vertex = a corner where two sides meet.
• Number of sides = number of vertices, always.
• Triangle 3, square/rectangle 4, pentagon 5, hexagon 6.
• Circle is not a polygon (no vertices, no straight sides).