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Lesson 3-4 Polygons Modified by Lisa Palen

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These figures are not polygonsThese figures are polygons Definition:A closed figure formed by a finite number of coplanar segments so that each segment intersects exactly two others, but only at their endpoints. Polygons

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Regular:A polygon in which all angles are congruent and all sides are congruent That’s an equiangular equilateral polygon. Irregular: A polygon that is not regular Classifications of a Polygon

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Convex: A polygon with no angles measuring more than 180 No line containing a side of the polygon contains a point in its interior Concave: A polygon that has at least one angle that measures more than 180 (a reflex angle) A polygon for which there is a line containing a side of the polygon and a point in the interior of the polygon. Has no indentations. Like a cave. Has indentations.

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Polygon Names 3 sidesTriangle 4 sides 5 sides 6 sides 7 sides 8 sides Nonagon Octagon Heptagon Hexagon Pentagon Quadrilateral 10 sides 9 sides 12 sides Decagon Dodecagon n sides n-gon

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Diagonal of a Polygon a segment connecting nonconsecutive vertices of a polygon

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Interior Angle of a Polygon For example, ∆ ABC has interior angles: ABC, BAC, BCA The interior angles of a polygon are the angles inside the polygon, formed by two adjacent sides.

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Exterior Angle of a Polygon For example, ∆ ABC has exterior angle: ACD. It forms a linear pair with ACB. An exterior angle of a polygon is an angle that forms a linear pair with an interior angle. It is an angle outside the polygon formed by one side and one extended side of the polygon. A B C D Exterior Angle Interior Angles

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What is the sum of the measures of the interior angles of a 3-gon? m<A + m<B + m<C = 180 GeoGebra Applet at Geometry Online

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What is the sum of the measures of the interior angles of a convex 4- gon? 180 + 180 = 360 GeoGebra Applet at Geometry Online

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180 + 180 + 180 = 540 What is the sum of the measures of the interior angles of a convex 5- gon? GeoGebra Applet at Geometry Online

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What is the sum of the measures of the interior angles of a convex 6- gon? (a hexagon) 180 + 180 + 180 + 180 = 720 GeoGebra Applet at Geometry Online

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What is the sum of the measures of the interior angles of a regular n- gon?

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What is the sum of the measures of the interior angles of a convex n-gon? Polygon Number of Sides Sum of Measures of Interior Angles Triangle3180° Quadrilateral4360° Pentagon5540° Hexagon6720° n-gonn(n - 2)180°

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What is the measure of each interior angle of a regular 3- gon? 60

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What is the measure of each interior angle of a regular 4-gon? 90

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What is the measure of each interior angle of a regular 5-gon? 108

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What is the measure of each interior angle of a regular 6-gon? 120

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What is the measure of each interior angle of a regular n-gon?

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PolygonNumber of Sides Measure of Each Interior Angle Triangle360° Quadrilateral490° Pentagon5108° Hexagon6120° n-gonn(n - 2)180°/n

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What is the sum of the measures of the exterior angles of a 3- gon? (a triangle) Sum of Measures of Exterior Angles = 360

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What is the sum of the measures of the exterior angles of a 4- gon? (a quadrilateral) Sum of Measures of Green Angles = 360 GeoGebra Applet at Geometry Online

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What is the sum of the measures of the exterior angles of a 5- gon? (a pentagon) GeoGebra Applet at Geometry Online Sum of Measures of Green Angles = 360

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What is the sum of the measures of the exterior angles of a 6- gon? (a hexagon) Sum of Measures of Green Angles = 360 GeoGebra Applet at Geometry Online

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What is the sum of the measures of the exterior angles of a convex n-gon? Yes, always, no matter what n is!

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What is the sum of the measures of the exterior angles of a convex n-gon? PolygonNumber of Sides Sum of Measures of Exterior Angles Triangle3360° Quadrilateral4360° Pentagon5360° Hexagon6360° n-gonn360°

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What is the measure of each exterior angle of a regular 3-gon? ? ? ?

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What is the measure of each exterior angle of a regular 4-gon? ? ? ? ?

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What is the measure of each exterior angle of a regular 5-gon? ? ? ? ? ?

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What is the measure of each exterior angle of a regular 6-gon? ? ? ? ? ? ?

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What is the measure of each exterior angle of a regular n-gon?

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PolygonNumber of Sides Measure of Each Exterior Angle Triangle3120° Quadrilateral490° Pentagon572° Hexagon660° n-gonn360°/n

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For a convex polygon with n sides: The sum of the measures of the interior angles is The measure of one interior angle is The sum of the measures of the exterior angles is The measure of one exterior angle is For a regular polygon with n sides:

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