1. Unit 9. Day 7.

2. Draw a circle like this.
Segment 𝐴𝐶 or 𝐴𝐶 𝐴
radius 𝑟 𝐶

3. Draw a circle like this.
Segment 𝐴𝐵 or 𝐴𝐵 𝐴 𝐶 𝑑
diameter 𝐵

5. Circumference vs. Diameter

6. 𝐶 = 𝜋 ∙ 𝑑 Example A: Measure the diameter of each circle.
Measure the distance around the circle (string).
Compare these values 𝐶 = 𝜋 ∙ 𝑑
You should have noticed that…
circumference
…the distance around the circle is slightly more than 3 times the diameter. … 𝜋

7. 𝐶=𝜋𝑑
𝐶≈ 𝑑
3.14
22 7
𝐶≈ 𝑑

8. 𝐶=𝜋𝑑 𝐶=3.14∙𝑑 𝐶= 22 7 ∙𝑑 𝐶= 21𝜋 𝑐𝑚 𝐶= 65.94 𝑐𝑚 𝐶= 66 𝑐𝑚 65.973446 𝑐𝑚
Example B: Find the circumference using each formula.
𝐶= 22 7 ∙𝑑
𝐶=𝜋𝑑
𝐶=3.14∙𝑑 3
𝐶= 22 7 ∙
21 1
𝐶=𝜋∙ 21 𝑐𝑚
𝐶=3.14∙ 21 𝑐𝑚 21 𝑐𝑚 1 𝐶=
21𝜋 𝑐𝑚 𝐶=
65.94 𝑐𝑚 𝐶=
66 𝑐𝑚 𝑐𝑚

9. 𝐶=𝜋𝑑 𝐶=3.14∙𝑑 𝐶= 22 7 ∙𝑑 𝐶= 91𝜋 𝑓𝑡 𝐶= 285.74𝑓𝑡 𝐶= 286 𝑓𝑡 285.88493 𝑓𝑡
Example C: Find the circumference using each formula.
𝐶= 22 7 ∙𝑑
𝐶=𝜋𝑑
𝐶=3.14∙𝑑
𝐶= 22 7 ∙
91 1 13
𝐶=𝜋∙ 91 𝑓𝑡
𝐶=3.14∙ 91 𝑓𝑡 91 𝑓𝑡 1 𝐶=
91𝜋 𝑓𝑡 𝐶=
285.74𝑓𝑡 𝐶=
286 𝑓𝑡 𝑓𝑡

10. 𝐶=𝜋𝑑 𝐶=3.14∙𝑑 𝐶= 22 7 ∙𝑑 35 2 𝜋 𝑚 𝐶= 109.9 𝑚 54.95 𝑚 𝐶= 110 𝑚 55 𝑚 𝐶=
Example D: Find the circumference using each formula.
𝐶= 22 7 ∙𝑑
𝐶=𝜋𝑑
𝐶=3.14∙𝑑 11 5
35 2
𝐶= 22 7 ∙
35 1
35 2
35 2 35 𝑚
𝐶=3.14∙ 𝑚 𝑚
𝐶=𝜋∙ 35 1 1
35 2 𝜋 𝑚 𝐶= 𝑚 𝑚 𝐶=
110 𝑚
55 𝑚 𝐶=
35𝜋 𝑚 𝑚

12. 𝐶=𝜋𝑑 𝐶=3.14∙𝑑 𝐶= 73.476 𝑐𝑚 𝐶=73. 5 𝑐𝑚 73.513268 𝑐𝑚 𝐶=3.14∙ 23.4 11.7
Example E: The radius of a paper plate is 11.7 cm. Find the circumference to the nearest tenth. (Use 3.14 as an approximation for 𝜋.)
𝐶=𝜋𝑑
𝐶=3.14∙𝑑
𝐶=3.14∙
23.4
11.7 𝑐𝑚 𝐶= 𝑐𝑚
𝐶=73. 5 𝑐𝑚 𝑐𝑚

13. 𝐶=𝜋𝑑 𝐶=3.14∙𝑑 ÷2 𝑃 = 20.56 𝑚 12.56 + 8 𝐶= 25.12 𝑚 25.12 𝑚 𝐶=3.14∙ 8 𝑚
Example F: The figure below is in the shape of a semicircle. Find the perimeter of the shape. (Use 3.14 for 𝜋.)
𝐶=𝜋𝑑
𝐶=3.14∙𝑑
𝐶=3.14∙ 8 𝑚 𝐶=
25.12 𝑚
25.12 𝑚 ÷2 𝑃 =
20.56 𝑚
12.56
+ 8