# UNIT 06: POLYGONS

## 00. MAIN ELEMENTS

A polygon is the portion of the plane bounded by a closed polyline. A polygon is a plane shape with straight sides. A plane is a flat surface with no thickness.
Polygons are 2-dimensional shapes. They are made of straight lines, and the shape is “closed” (all the lines connect up).

## MAIN ELEMENTS.

• Side: Any of the segments which form the polygon.
• Vertex: It is the point where the sides meet. The number of vertices and sides is the same.
• Diagonal: It is any of the segments which join two vertices non consecutive.
• Internal angle: It is formed by two consecutive sides.
• External angle: It is formed by one side and the extension of the other consecutive.

If you look at the figure, an exterior angle and its adjacent interior are adjacent, this means, they are consecutive and also add up to 180 º:

## CLASSIFICATION BY NUMBER OF SIDES.

 Number of sides Name of the polygon 3 Triangle 4 Quadrilateral 5 Pentagon 6 Hexagon 7 Heptagon 8 Octagon 9 Nonagon 10 Decagon 11 Hendecagon 12 Dodecagon