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Classifying Polygons
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PolygonA polygon is a closed figure made by joining line segments, where each line segment intersects exactly two others. Examples: The following are examples of polygons:
The figure below is NOT a polygon, since it is not a closed figure:
The figure below is NOT a polygon, since it is not made of line segments:
The figure below is NOT a polygon, since its sides do not intersect in exactly two places each:
Sides Vertex
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ConvexIf the sides extend, no points lie in the interior of the polygonConcaveIf the sides extend, points will lie in the interior
Example: The following figures are convex.
The following figures are concave (not convex). Note the line segment drawn between two points inside the figure that also passes outside of the figure.
* Note: All Theorems in this chapter deal with convex polygons
http://www.classzone.com/cz/books/geometry_2011_na/resources/applications/animations/explore_learning/dswmedia/anm539/anm539.html
Try this activity from classzone.com
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Polygons named by the number of sides they have.
Numberof Sides
Type ofpolygon
3
4
5
6
7
8
9
10
12
n
triangle
quadrilateral
pentagon
hexagon
heptagon
octagon
nonagon
decagon
dodecagon
ngon
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Diagonal Connects 2 nonconsecutive vertices
How many diagonals are there?
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Regular Polygon equiangular and equilateral
Examples:
Equilateral Equiangular Regular
1.) The head of a bolt is shaped like a regular hexagon. The expressions shown represent side lengths of the hexagonal bolt. Find the length of a side.
(4x + 3) mm
(5x 1) mm
2.) Classify the polygon by the number of sides. Tell whether the polygon is equilateral, equiangular, or regular.
3.) The expressions (4x + 8)0 and (5x 5)0 represent the measures of 2 of the congruent angles in example 2. Find the measure of an angle.
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http://www.math.com/school/subject3/practice/S3U2L1/S3U2L1Pract.html
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Homework
p. 4447/113(do not explain 810), 1529 Odd, 3237, 39