The document provides an overview of polygons, which are closed shapes in a plane with three or more sides. It distinguishes between convex and concave polygons, as well as regular and irregular polygons, and classifies them according to the number of their sides. Specific types of polygons such as triangles, quadrilaterals, pentagons, hexagons, heptagons, octagons, nonagons, and decagons are defined.

1. POLYGONS
Understanding the properties of various
shapes, or figures, is going to be key
throughout Geometry.
In this lesson, we will explore some of these
shapes, more formerly known as polygons.
Sara Reyes
CSE 684
Spring 2012

2. LEARNING
OBJECTIVES
First, to distinguish between
convex and concave polygons.
Next, to distinguish between
regular and irregular
polygons.
Lastly, to classify polygons
according to how many sides
they have.

3. WHAT ARE POLYGONS?
Closed shapes or figures in a plane with
three or more sides.
Alternatively, a polygon can be defined as
a closed planar figure that is the union of
a finite number of line segments.
The term polygon is derived from a Greek
word meaning “many-angled”.

4. WHAT HAVE WE
COVERED SO FAR?
 Distinguish between convex and concave polygons
Distinguish between regular and irregular
polygons
Classify polygons according to the number of sides
they have
o classify polygons according to how many they
have

5. Convex polygon- A
polygon for which any two
interior points can be
connected by a line
segment that stays entirely
inside the polygon.
Concave polygon- A polygon
that is not convex. A line
segment connecting two points
may pass outside the figure.
“CAVED IN”

6. REGULAR VS.
IRREGULAR POLYGONS
A regular polygon is a
polygon in which all the
angles and sides are equal.
An irregular polygon is a
polygon whose sides are not
the same length or whose
interior angles do not all
have the same measure.

7. SO, WHAT HAVE WE
COVERED SO FAR?
 Distinguish between convex and concave polygons
 Distinguish between regular and irregular polygons
Classify polygons according to the number of sides they have
o classify polygons according to how many they have

8. WHAT IS A TRIANGLE?
A triangle, sometimes called a trigon, is a three-
sided polygon.

9. WHAT IS A QUADRILATERAL?
A quadrilateral is a four-sided polygon.

10. WHAT IS A PENTAGON?
A pentagon is a five-sided polygon.

11. WHAT IS A HEXAGON?
A hexagon, also referred to as a sexagon, is
a six-sided polygon.

12. WHAT IS A HEPTAGON?
A heptagon, also referred to as a septagon, is a
seven-sided polygon.

13. WHAT IS A OCTAGON?
An octagon is a eight-sided polygon.

14. WHAT IS A NONAGON?
A nonagon is a nine-sided polygon.

15. WHAT IS A DECAGON?
A decagon is a ten-sided polygon.