2. By Renikki Alexander IDT 7062

3. Let’s Listen to the Circle Song "πr 2 sounds like area to me and when I need circumference I'll use πd."

4. Let’s Start with Vocabulary Circle Center Diameter Radius Circumference Pi

5. This is a circle and its center. Center Course 1 A circle is the set of all points in a plane that are the same distance from a given point. The center is the given point from which all points on a circle are the same distance.

6. What is the radius? The radius is a line segment with one endpoint at the center of the circle and the other endpoint on the circle is a radius ( The plural form for radius is radii. Center Radius Course 1

7. Diameter A diameter is a chord that passes through the center of the circle. Center Radius Diameter

8. Radius The diameter is twice the size of the radius. The formula for diameter is 2r. You will multiply 2 times the value of the radius, which is r. The radius is half the size of the diameter. The formula for radius is r = d. 2 You will replace d with the value of the diameter and divide by 2.

9. The distance around a circle is called the circumference. Center Radius Diameter Circumference

10. What is pi? Pi is the ratio of the circumference of a circle to the diameter and pi equals 3.14

11. Let’s try Naming the Parts of a Circle N LM is a diameter. ZL, ZM, and ZN are radii. The center is Z. M Z L

12. How To Calculate Circumference Example 1 The formula for the circumference of a circle is C =  d, or C = 2  r. Remember to use 3.14 for  (pi) 11 ft C =  d Write the formula C = 3.14 (11) Replace  with 3.14 and d with 11 C = 34.54 ft

13. How To Calculate Circumference Example 2 The formula for the circumference of a circle is C =  d, or C = 2  r. Remember to use 3.14 for  (pi) C = 2  r Write the formula C = 2 (3.14) (5) Replace  with 3.14 and r with 5 C = 31.4 cm 5 cm

15. a. Center b. Diameter c. Circumference d. Radius

18. a. Diameter b. Center c. Pi d. Radius

21. a. C =  d or C = 2  r b. C = 2d c. C = 2d or C =2r d. C = d 2

24. a. 22.5 in b. 30 in c. 15 in d. 47.1 in 15 inches

27. a. 9.42 cm b. 18.84 cm c. 3 cm d. 12.54 cm 3 cm