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# CPM Geomety Unit 9 D1&2

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This PPT explains how to name various polygons and also explains how to find the angles of polygons

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### CPM Geomety Unit 9 D1&2

1. 1. Unit 9 Day 1 & 2
2. 2. Polygons <ul><li>These are Polygons </li></ul>
3. 3. Polygons <ul><li>These are NOT polygons </li></ul>
4. 4. Polygon <ul><li>Definition – </li></ul><ul><ul><li>A two-dimensional closed figure made up straight line segments connected end to end. They may not cross (intersect) at any other points. </li></ul></ul>Polygon or not?
5. 5. Names of Polygons Number of Sides Name of Polygon 3 4 5 6 7 8 9 10 11 n Number of Sides Name of Polygon Triangle Quadrilateral Pentagon Hexagon Heptagon Octagon Nonagon Decagon 11-gon n-gon
6. 6. US – 2 Summary
7. 7. Convex Concave <ul><li>Examples convex </li></ul><ul><li>Examples concave </li></ul>
8. 8. Regular Polygon <ul><li>Definition </li></ul><ul><ul><li>A convex polygon with all angles congruent and all sides congruent. </li></ul></ul>
9. 9. Find the sum of the interior angles of a 100-gon. <ul><li>(100 – 2)180 = 17,640 </li></ul><ul><li>If the 100-gon is a regular polygon, what is the measure of each angle? </li></ul><ul><li>17,640/100 = 176.4 º </li></ul>
10. 10. Formula to find an angle of a regular n-gon.
11. 11. Practice <ul><li>Find an angle of a regular heptagon </li></ul><ul><li>Find an angle of a regular 21-gon </li></ul>
12. 12. Working backwards <ul><li>How would you find the number of sides of a polygon if the sum of their interior angles is 1440 º? </li></ul>
13. 13. Find the number of sides <ul><li>900 º </li></ul><ul><li>1980º </li></ul><ul><li>1860º </li></ul>
14. 14. Homework US 8, 9, 21, 22, 24, 25