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Do Now

Do Now. Pg. 537 #1-5 Odds. 3 / 20 /2014 9-2 B Circles. HAPPY SPRING!!!. Center. Circle- the set of all points in a plane that are the same distance from a given point, called the center . . Radius. Center.

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Do Now

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  1. Do Now Pg. 537 #1-5 Odds

  2. 3/20/2014 9-2 B Circles HAPPY SPRING!!!

  3. Center Circle- the set of all points in a plane that are the same distance from a given point, called the center.

  4. Radius Center Radius(plural: radii). A line segment with one endpoint at the center of the circle and the other endpoint on the circle.

  5. Radius Center Diameter Diameter-a chord that passes through the center of the circle. - the longest chords in a circle.

  6. Radius Center Chord Diameter Chord-a line segment that has both endpoints on the circle.

  7. The circle is circle Z. LM is a diameter. LN and LM are chords. ZL, ZM, and ZN are radii. Example 1 Name the circle, a diameter, and three radii. L Z M N

  8. Circumference Radius Center Diameter The distance around a circle -circumference.

  9. The ratio of the circumference to the diameter, , is the same for any circle. This ratio is represented by the Greek letter , which is read “pi.” C d C =  d

  10. The decimal representation of pi starts with 3.14159265 . . . and goes on forever without repeating. Most people estimate  using either 3.14 or . 22 7 The formula for the circumference of a circle is C = d, or C = 2r.

  11. Key Concept

  12. Key Concept

  13. 8 ft C = d C 3•8 C 24 ft Example 2 A skydiver is laying out a circular target for his next jump. Estimate the circumference of the target by rounding  to 3. Write the formula. Replace  with 3 and d with 8.

  14. C = d C 3.14•11 C 34.54 ft Example 3 Find the missing value to the nearest hundredth. Use 3.14 for pi. d = 11 ft; C = ? 11 ft Write the formula. Replace  with 3.14 and d with 11.

  15. C = 2r C 2 •3.14 •5 C 31.4 cm Example 4 Find each missing value to the nearest hundredth. Use 3.14 for pi. r = 5 cm; C = ? 5 cm Write the formula. Replace  with 3.14 and r with 5.

  16. 21.983.14d 21.983.14d _______ _______  3.143.14 7.00 cm d Example 5 Find each missing value to the nearest hundredth. Use 3.14 for pi. C = 21.98 cm; d = ? C = d Write the formula. Replace C with 21.98 and with 3.14. Divide both sides by 3.14.

  17. Example 6 The diameter of a circle is 48 centimeters. Find the radius. The radius is 24 centimeters.

  18. Example 7 The radius of a circle is 9 inches. Find the diameter. d= 2r d = 2 ● 9 d = 18 The diameter is 18 inches.

  19. Example 8 John is making a table that has a top with a diameter of 24 inches. Find the circumference of the table. Round to the nearest tenth. C = d C ≈ 3.14(24) C ≈ 75.36 The distance around the table is about 75.36 inches.

  20. Your Turn!

  21. Find the circumference of each circle. Use 3.14 for . 1.2. 3. Find the circumference of a circle with adiameter of 20 feet. Use 3.14 for . 3 in. 8 in. C = 25.12 in. C = 18.84 in. 62.8 ft

  22. 1. Identify the circumference of the given circle. Use 3.14 for . A. 31.14 in. B. 31.21 in. C. 31.33 in.D. 31.4 in. 10 in.

  23. 2. Identify the circumference of the given circle. Use 3.14 for . A. 37.54 in. B. 37.68 in. C. 37.81 in.D. 37.93 in. 6 in.

  24. 3. Identify the circumference of a circle with a diameter of 26 feet. Use 3.14 for . A. 81.64 ft B. 81.73 ft C. 81.86 ftD. 81.92 ft

  25. Homework • PRACTICE RAPS!!!!!!!!!!

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