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Section 3.4
Exploring Polygons
Thompson
•Convex vs. Concave
Polygons
•Parts of a Polygon
•Classifying Polygons
•W/ some triangle review
Exploring
 Polygons are many-sided figures, with
sides that are line segments. Polygons
are named according to the number of
sides and angles they have.
 Can be “regular” – all sides and all
angles are equal to each other
 Two sides of equal
length
 Three acute angles
 Sum of angles =
180°
 All sides equal
length
 Three acute angles
 Sum of angles =
180°
 Is a regular polygon
 No sides are equal
 No angles are equal
 May have obtuse
angle
 Sum of angles =
180°
 Opposite sides are parallel
 Opposite side are equal in length
 Each angle equals 90°
 Sum of angles = 360°
 All sides equal
 All angles equal and are 90 ° each
 Sum of angles = 360 °
 Is a regular polygon
 Two sides are parallel
 Has obtuse and acute angles
 Sometimes has a right angle
 Sum of angles = 360 °
 All four sides of equal length
 Opposite angles are equal – 2 acute angles,
2 obtuse angles
 Sum of angles = 360 °
 Regular polygon
 Opposite sides parallel
 Opposite sides equal in length
 Opposite angles equal
 Sum of angles = 360 °


5 sides
Regular polygon


6 sides
Can be regular polygon


8 sides
Can be regular polygon


10 sides
Can be regular polygon
Where do we see
Regular
Polygons in real
Life?
Proof
Convex or Concave?
A Polygon is a plane figure formed by three or
more segments.
A Polygon can either be convex or concave.
If a polygon is convex then no sides go through the interior of the polygon.
(All vertices point outside the polygon.)
If a polygon is concave then it is not convex. A side goes through the interior of the
polygon.
(At least one vertex points inside the polygon.)
Example 1:
Which figures are polygons?
Example 1:
Which figures are polygons?
polygon
polygon
polygon
polygon
Example 2:
Label the polygons as convex or concave?
Example 2:
Label the polygons as convex or concave?
convex
concave
concave
convex
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Sides
Interior Angles
Perimeter
Exterior Angles
Area
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices











Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Interior Angles
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Interior Angles
Exterior Angles
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Sides
Interior Angles
Exterior Angles
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Sides
Interior Angles
Perimeter
Add all sides
Exterior Angles
Parts of a polygon
The simplest polygon is a triangle. Many of the
terms you learned about a triangle apply to all
polygons. Remind yourself of what the following
terms mean.
Vertices
Sides
Interior Angles
Perimeter
Exterior Angles
Area
Parts of a polygon
In more complex polygons there are more parts.
Learn these new terms:
Consecutive
Diagonal
Regular
Parts of a polygon
In more complex polygons there are more parts.
Learn these new terms:
Consecutive
Diagonal
Refers to parts that are right next to each other.
(They share a common vertex or side.)
Regular
Parts of a polygon
In more complex polygons there are more parts.
Learn these new terms:
Consecutive
Diagonal
Joins two nonconsecutive vertices.
(Notice the triangle does NOT have any diagonals.)
Regular
Parts of a polygon
In more complex polygons there are more parts.
Learn these new terms:
Consecutive
Diagonal
A polygon that is equilateral and equiangular.
Regular
Classifying Polygons
A Polygon is classified by its’ number of sides.
Number of Sides
3
4
5
6
7
8
9
10
12
n
Type of Polygon
Triangle
Quadrilateral
Pentagon
Hexagon
Heptagon
Octagon
Nonagon
Decagon
Dodecagon
n - gon (click here for more)
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