Geometry Session 3: Polygons

Session 3, Part A:
Hidden Polygons (20 minutes)

In This Part: Identifying Polygons | Finding Polygons

Polygons are two-dimensional geometric figures with these characteristics:

•	They are made of straight line segments.
•	Each segment touches exactly two other segments, one at each of its endpoints.
•	They are closed -- they divide the plane into two distinct regions, one "inside" and the other "outside" the polygon.

These shapes are polygons:

Polygons

These shapes are not polygons:

Problem A1

Look at the shapes above that are not polygons. Explain why each of these shapes does not fit the definition of a polygon.

Polygons can be classified according to the number of sides they have. Note 2

Name

# of Sides

Examples

Triangle		3

Quadrilateral		4

Pentagon		5

Hexagon		6

Heptagon		7

Octagon		8

Nonagon		9

Decagon		10

Polygons with more than 10 sides are not usually given special names. A polygon with 11 sides is described as an 11-gon, a polygon with 12 sides as a 12-gon, and so on. Each of the polygons below is a 17-gon.

17gon

When people talk about a general polygon -- one where you don't know the exact number of sides -- they often refer to it as an n-gon.

Hidden Polygons and the Video Segment problem adapted from IMPACT Mathematics, developed by Educational Development Center, Inc. pp. 42-45. © 2000 Glencoe/McGraw-Hill. Used with permission. www.glencoe.com/sec/math

Next > Part A (Continued): Finding Polygons

Session 3: Index | Notes | Solutions | Video