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8-5 Classifying Polygons
Course 2
Warm UpWarm Up
Problem of the DayProblem of the Day
Lesson PresentationLesson Presentation
Course 2
8-5 Classifying Polygons
Warm Up
1. How do you name a ray? Under the raysymbol, name first the endpoint and thenany other point on the ray.
2. What is the measure of an obtuse angle?between 90° and 180°
3. How do you name a line?Under the line symbol, name any twopoints on a line.
4. What is true of supplementary angles?The sum of their measures is 180°.
Problem of the Day
Draw a polygon with 10 congruent sides. Make 5 of the angles acute angles and the other 5 reflex angles (greater than 180°).
Possible answer:
Course 2
8-5 Classifying Polygons
Learn to identify and name polygons.
Course 2
8-5 Classifying Polygons
Vocabulary
polygonregular polygon
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Course 2
8-5 Classifying Polygons
Triangles and rectangles are examples of polygons. A polygon is a closed plane figure formed by three or more line segments. Each line segment forms a side of the polygon, and meets, but does not cross, another line segment at a common point. This common point is a vertex of a polygon.
The polygon atleft has sixsides and sixvertices.
Vertices is plural for vertex.
Remember!
Side
Vertex
Course 2
8-5 Classifying Polygons
Determine whether each figure is a polygon. If it is not, explain why not.
Additional Example 1: Identifying Polygons
A. B.
The figure is a polygon. It is a closed figure with 4 line segments.
The figure is not a polygon. It is not a closed figure.
Course 2
8-5 Classifying Polygons
Determine whether each figure is a polygon. If it is not, explain why not.
Additional Example 1: Identifying Polygons
C. D.
The figure is not a polygon. The figure is not formed by line segments.
The figure is not a polygon. There are line segments in the figure that intersect.
Course 2
8-5 Classifying Polygons
Determine whether each figure is a polygon. If it is not, explain why not.
Check It Out: Example 1
A. B.
The figure is a polygon. It is a closed figure with 5 line segments.
The figure is not a polygon. It is not a closed figure.
Course 2
8-5 Classifying Polygons
Determine whether each figure is a polygon. If it is not, explain why not.
Check It Out: Example 1
C. D.
The figure is not a polygon. The figure is not formed by line segments.
The figure is not a polygon. There are line segments in the figure that intersect.
Course 2
8-5 Classifying Polygons
Polygons are classified by the number of sidesand angles they have.
Triangle3 sides
3 angles
Quadrilateral4 sides
4 angles
Pentagon5 sides
5 angles
Hexagon6 sides
6 angles
Heptagon7 sides
7 angles
Octagon8 sides
8 angles
Nonagon9 sides
9 angles
Decagon10 sides
10 angles
Course 2
8-5 Classifying Polygons
Name each polygon.
Additional Example 2: Classifying Polygons
A.
Octagon
B.
Quadrilateral
Course 2
8-5 Classifying Polygons
Check It Out: Example 2
Name each polygon.
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A. B.
Quadrilateral Pentagon
Course 2
8-5 Classifying Polygons
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A regular polygon is a polygon in which all sides are congruent and all angles are congruent.
Course 2
8-5 Classifying Polygons
Additional Example 3: Identifying and Classifying Regular Polygons
Name each polygon and tell whether it is aregular polygon. If it is not, explain why not.
The figure is a regularquadrilateral. A regular quadrilateral is also called a square.
The figure is aquadrilateral. It is not a regular polygon becauseall of the sides are not congruent.
A. B.
Course 2
8-5 Classifying Polygons
Check It Out: Example 3
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The figure is a triangle. It is not a regular polygon because all sides and angles are not congruent.
The figure is a regular triangle.
Name each polygon and tell whether it is aregular polygon. If it is not, explain why not.
A. B.
Course 2
8-5 Classifying Polygons
Homework
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Course 2
8-5 Classifying Polygons
Textbook PG 468 1-18
Lesson Quiz: Part II
Determine whether each figure is a polygon. If it in not, explain why not. Name each polygon.
4.
5. Tell whether each figure above is a regular t polygon. If it is not, explain why not.
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no; curved lines
1: No, all sides and angles are not congruent.2, 4: No, they are not polygons.3: Yes
Course 2
8-5 Classifying Polygons
