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Circumference and Area of Circles

Circumference and Area of Circles. Parts of a Circle. Radius-Straight line from the middle to the outside of a circle. Diameter-a line that cuts the circle in half from end to end. Circumference. Circumference is the distance around the circle. Like the perimeter. Pi.

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Circumference and Area of Circles

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  1. Circumference and Area of Circles

  2. Parts of a Circle • Radius-Straight line from the middle to the outside of a circle

  3. Diameter-a line that cuts the circle in half from end to end

  4. Circumference • Circumference is the distance around the circle. Like the perimeter.

  5. Pi • Pie is a special number. It is the ratio of the circumference to the diameter

  6. Pi goes on forever!!!!!!!!!!! • We approximate it using 3.14

  7. Finding Circumference

  8. Finding Circumference 6 · 3.14 = 18.84 in. 6𝛑 in. would be the exact answer, but we are going to estimate using 𝛑 = 3.14

  9. C=pi*3 C= 9.42 in

  10. C=pi*12 C= 37.70 in

  11. What if you have the radius? The radius is half of the diameter C=25.13

  12. Find the area C= 4 * pi C = 12.57

  13. How Would You Find the Diameter if You Only Had the Circumference? Diameter= 10.19 in

  14. Area of a Circle The Formula

  15. Example 3.14 · 36 = 113.04 in²

  16. Try

  17. Try

  18. What if you are given the diameter? • How can you find the radius if you only have the diameter? • The radius is half of the diameter • Diameter = 8 then radius =4

  19. Example Radius = 3

  20. Try

  21. Finding Radius and Diameter from Area • Just like you could find radius and diameter from circumference, you can find the radius and diameter from area by filling in known values and solving.

  22. Example Area = 𝛑r² Area = 78.50 cm² Radius = Diameter =

  23. Area = 314.00 cm² Radius = Diameter =

  24. Area = 200.96 cm² Radius = Diameter =

  25. Closure • What is the formula for finding the area of a circle?

  26. Closure • How can you find the radius if you only have the diameter?

  27. Closure • What is the diameter?

  28. Closure • What is the radius?

  29. Closure • What is circumference?

  30. Closure • What is the relationship between the radius and the diameter?

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