1. Circumference and Area of a Circle

2. Diameter Radius centre What is the formula relating the circumference to the diameter?

3. Radius What is the formula to find Circumference? C=2 ∏ r constant pi radius

4. Diameter of Earth is 7,926.41 miles To find circumference use C=2∏ r First divide Diameter by 2 to get r. C=2∏∙3963.2 C= 7,926.41∏ Lets find the circumference of the Earth!

5. Now that we know how to find circumference, lets find the area. o What do we need to find area? o All we need to find the area of a circle is the radius! So what is the formula? A= 3.14r²

6. So lets see if we can find the area of the moon. What is the only thing we need? 1 737.4 kilometers Ok lets plug that in to the formula. A= (3.14)(1737.4)² A=(3.14)(3018558.8) A=9478274.5 Square r Multiply

7. You Do! What is the Circumference of a circle with a radius of 10 in.? What is the area of a circle with a radius of 10 in.?

8. And the answer is…. 62.8 Go back to questions!

9. And the answer is…. 314

10. Why does all this matter? http://www.youtube.com/watch?v=knfVUOTcJrQ