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# At a Glance - Polygons

A polygon is any closed figure with three or more straight sides. "Closed" means that there are no gaping holes in it and that all sides connect together.

## These Are Not Polygons:

That's right, a circle is not a polygon. It doesn't have all the properties, and it's really hard to count the number of sides.

## Names of Some Common Polygons

 Number of Sides Number of Angles Name 3 3 Triangle 4 4 Quadrilateral 5 5 Pentagon 6 6 Hexagon 7 7 Septagon (or Heptagon) 8 8 Octagon 9 9 Nonagon 10 10 Decagon 12 12 Dodecagon

## Important Vocabulary

Polygons have a lot of important vocabulary terms that come with them. You will need to memorize these, but don't worry, they aren't too difficult.

• Angle: the shape formed when two rays meet at a common point. AKA "the corner."
• Vertex: the point where two rays meet; the corner point of a polygon. The plural of vertex is vertices.
• Side: the straight edge of a polygon.

• Equiangular: a figure where all angles are equal in measure.
• Equilateral: a figure where all sides are equal in length.
• Regular Polygon: an equilateral, equiangular polygon.

## Regular Polygons

You're probably familiar with these shapes

## Base and Height of a Polygon

• Base: the bottom side of a polygon.
• Height: the height of a polygon is the perpendicular distance from the top-most vertex to the base. The height and base ALWAYS form a right angle.

#### Exercise 1

Which of the following look like regular polygons?

#### Exercise 2

How many vertices does the following polygon have?

#### Exercise 3

Which two sides form the height and base of the polygon?