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Review The lengths of three sides of a triangle are given. Classify the triangle. 1. 12, 12, 12 2. 18, 10, 14 3. 15, 15, 26 equilateral scalene isosceles

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Vocabulary polygon regular polygon diagonal

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A polygon is a closed plane figure formed by three or more line segments. A regular polygon is a polygon in which all sides are congruent and all angles are congruent. Polygons are named by the number of their sides and angles.

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You can divide any quadrilateral into two triangles by drawing a diagonal, a line segment that connects two non-adjacent vertices. The sum of the interior angle measures in a triangle is 180°, so the sum of the interior angle measures in a quadrilateral is 360°.

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Tell whether each shape is a polygon. If so, give its name and tell whether it appears to be regular or not regular. polygonpentagon not regular

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Tell whether each shape is a polygon. If so, give its name and tell whether it appears to be regular or not regular. octagonregular polygon

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Tell whether each shape is a polygon. If so, give its name and tell whether it appears to be regular or not regular. quadrilateral regular

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Tell whether each shape is a polygon. If so, give its name and tell whether it appears to be regular or not regular. quadrilateral not regular

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720° The prefixes in the names of the polygons tell you how many sides and angles there are. tri- = threequad- = four penta- = fivehexa- = six octa- = eight Reading Math

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1. Name each polygon and tell whether it appears to be regular or not regular. 2. What is the measure of each angle in a regular dodecagon (12-sided figure)? 150° nonagon, regular; octagon, not regular

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1. Name the polygon and tell whether it appears to be regular or not regular. A. pentagon, not regular B. hexagon, regular C. heptagon, regular D. octagon, not regular

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2. What is the measure of each angle in a regular decagon (10-sided figure)? A. 108 B. 144 C. 150 D. 140

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The four angles create 360° 360 ÷ 4 = 90° Exterior angle is 90°

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The five angles create 360° 360 ÷ 5 = 72° Exterior angle is 72°

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Exterior angle = 360° ÷ number of angles

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CCalculate the angles marked with letters 100° 66° A 98° 91° 80° 75° B 95° 90° 57° 33° 25° 85° C

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