1. Lesson 6-9 Pages 275-277 Geometry: Circles and Circumference (and Area) Lesson Check 6-8

2. What you will learn! How to find the circumference of circles.

3. CircleCenter Diameter Radius Circumference

4. What you really need to know! A circle is the set of all points in a plane that are the same distance from a given point, called the center.

5. What you really need to know! The diameter d is the distance across the circle through its center. The radius r is the distance from the center to any point on the circle.

6. What you really need to know! The circumference C is the distance around the circle.

7. Radius Diameter Chord

8. What you really need to know! For every circle, C ÷ d is always equal to 3.1415926…. This number is represented by the Greek letter  (pi).

9. What you really need to know! We will use 3.14 for .

10. What you really need to know! The circumference C of a circle is equal to its diameter d times , or 2 times its radius r times . C =  d or C = 2  r

11. What you really need to know! The Area A of a circle is equal to  times r 2. A =  r 2 or A =  rr Demonstration

13. 1.Identify radius and diameter. 2.Use   d to find the Circumference. 3.Use   r  r to find Area.

14. Example 1: Find the circumference around the hamster’s running wheel. Round to the nearest tenth. r = 3 inches C = 2  r C = 2 3.14 3 C = 18.8 in

15. Example 1: Find the area inside the hamster’s running wheel. Round to the nearest tenth. A =  r 2 A =  r r A = 3.14 3 3 A = 28.3 in 2

16. Example 2: Find the circumference of a circle with a diameter of 49 centimeters. d = 49 cm r = 24.5 cm C = 2  r C = 2  3.14  24.5 C = 153.86 cm 49 cm

17. Example 2: Find the area of a circle with a diameter of 49 centimeters. d = 49 cm r = 24.5 cm A =  rr A = 3.14 24.5 24.5 A = 1884.785 cm 2 49 cm

18. Page 276 Guided Practice #’s 4-10

20. Pages 275-276 with someone at home and study examples! Read:

21. Homework: Page 277 #’s 12-22 even, 23, #’s 27-31 Lesson Check Ch 6

24. Page 579 Lesson 6-9

26. Study Guide and Review Pages 278-280 #’s 1-69 (Odd answers in back of book)

33. Prepare for Test! Page 281 #’s 1-25 Lesson Check Ch 6

36. Circle into Rectangle

37. Prepare for Test! Pages 282-283 #’s 1-15

48. A = L x W L = ½ x 2 x  x r W = r A = ½ x 2 x  x r x r A =  x r x r A =  r 2

49. C =  d or 2  r Circumference Area A =  r r

50. Circumference = 2  r Area =  r 2 or  rr  = 3.14 Radius

51. 1.Find the LCD. 2.Rewrite fractions using the LCD. 3.Add only the numerators, keeping the LCD. 4.Reduce to lowest terms.

52. The distance around a geometric figure.