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# Polygons

The word polygon has Greek roots and means "many sides" or "many
angles." A polygon is one of many plane shapes, which are defined as
figures that are closed, flat, and 2-dimensional having length and
width but no depth. Polygons are drawn using straight line segments
that only meet at their endpoints. Shapes that don't close, are not
straight line segments or do meet at points other than endpoints are
not classified as polygons.

Take a look at the examples below of shapes that are and are not
categorized as polygons:

It's good to note that while not all closed shapes are polygons, all
polygons are closed shapes.

## Names and sides of polygons

As you get to know more about polygons, it's good to learn their
names and sides since they play a major role in how you can identify
them. Every line segment in a polygon is known as a side. You can
identify polygons by the number of line segments or sides they
contain. For example, a pentagon is a polygon that has five sides
("penta" means "five" or "having five" and "-gon" refers to the
number of sides or angles).

Here is a quick overview of polygon names and their sides:

Name | Number of Sides |

Triangle | 3 |

Quadrilateral | 4 |

Pentagon | 5 |

Hexagon | 6 |

Heptagon | 7 |

Octagon | 8 |

Nonagon | 9 |

Decagon | 10 |

Hendecagon (or Undecagon, or Unidecagon) | 11 |

Dodecagon | 12 |

n -gon | n |

Are you confused about the n -gon? It's less confusing than you
might think. You might have noticed that, with the exception of the
triangle and
quadrilateral, all of the polygons listed above end in -gon. In truth, the
triangle is also called a trigon, and the quadrilateral is also
called a tetragon.

As mentioned previously, the suffix "-gon" refers to the side/angle
while its prefix identifies the number. So, using the example of the
pentagon, another way to write it would be 5-gon. If you want to
write heptagon similarly, you can write it as 7-gon since it has
seven sides. The triangle, or trigon, can be referred to as 3-gon
for its three sides. And the quadrilateral, or tetragon, can be
referred to as 4-gon. The term n -gon refers to a polygon with n
sides. In this case, the n can refer to any integer.

## Classifying polygons

Polygons fall under a variety of classifications based on their
sides and angles. Here are six polygon classifications:

- Regular polygons: All interior angles and sides of regular polygons are congruent (identical in form). An example of a regular polygon would be an equilateral triangle or square.
- Irregular polygons: Sides and angles of irregular polygons are not congruent. Examples of irregular polygons include rectangles, parallelograms, and right triangles.
- Convex polygons: Every interior angle of a convex polygon is less than 180 degrees. An example of a convex polygon would be a pentagon.
- Concave polygons: At least one interior angle of a concave polygon is greater than 180 degrees. A five-pointed star is an example of a concave polygon.
- Simple polygons: The sides of simple polygons don't intersect themselves and don't have holes. A square or hexagon is an example of a simple polygon.
- Complex polygons: The sides of complex polygons cross over each other at least one time. A pentagram is an example of a complex polygon.

## Practice questions on polygons

a. What is an example of a regular polygon?

A square

b. How many sides does a nonagon have?

9

c. A pentagon is an example of what type of polygon?

Convex polygon

d. What type of polygon could be referred to as a 6-gon?

Hexagon

e. Which polygon has 10 sides?

Decagon

f. Which polygons have interior angles and sides that are all
congruent (identical in form)?

Regular polygons

g. Which polygon is also known as a tetragon or 4-gon?

Square

## Topics related to the Polygons

## Flashcards covering the Polygons

## Practice tests covering the Polygons

## Get help learning about polygons

Polygons are shapes we encounter every day whether in the form of
triangles, squares, or octagons. But correctly naming, identifying,
and classifying them can sometimes be tough. The good news is your
student doesn't have to struggle to grasp polygons. There are tutors
eager to assist whether your student wants to simply gain a better
understanding of polygons or would like to go over these plane
shapes for an assignment or upcoming exam. If you want to learn more
about the benefits of tutoring for your student, reach out to the
Educational Directors at Varsity Tutors today.

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