2. 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

3. Vocabulary polygon regular polygon diagonal

4. 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.

5. 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°.

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

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

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

18. Exterior angle = 360° ÷ number of angles

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