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PolygonsPolygons
A closed figure formed by a finite number of coplanar segments such that:
1.The sides that have a common endpoint are noncollinear, and
2.Each side intersects exactly two other sides, but only at their endpoints
A polygon is named by the letters of its vertices, written in consecutive order.
Polygon ABC or CBA
Polygon WXYZ or YZWX, etc.
Polygon EFGHJK or HGFEKJ, etc.
Concave or ConvexConcave or Convex
There are two types of polygons:
Concave: Any side which is extended contains points in the interior of the polygon.
Convex: Any side which is extended contains no point in the interior of the polygon.
At least one side is “caved” in.
Special NamesSpecial NamesPolygons can be classified by the number
of sides they have:
Regular PolygonRegular Polygon
VUWVUTPWQPRQSRTSUT
UVWPQRST
A convex polygon in which all sides are congruent and all angles are congruent
Example 1Example 1
Number of Sides:
Name:
Convex or Concave?
Regular or Irregular?
Number of Sides:
Name:
Convex or Concave?
Regular or Irregular?
5
pentagon
Convex
Regular
8
Octagon
Concave
Irregular; WHY?
PerimeterPerimeter
The sum of the lengths of the sides of a polygon.
Some polygons have “shortcut” formulas:
Example 2Example 2
Example 3Example 3
First, use the distance formula to calculate the side lengths, then find the perimeter. 2
122
12 yyxxd
5254115 22 PQd
13168461 22 QRd
1.9828165 22 PRd
1.275131.9)( PQRP
Example 4Example 4
Draw a picture:
Define the variables:Width = w
Length = 3w
Width = w
Length = 3w
Perimeter of a rectangle:
wlP 22
w
ww
wwP
8
26
232
w
w
4
82Be sure to answer the question!Width = 4
Length = 3(4) = 12
HW: Page 49 (1 – 11 all; 13 – HW: Page 49 (1 – 11 all; 13 – 35 evens)35 evens)
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