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Determining Radius and Diameter

Determining Radius and Diameter. Ex 1) Find the radius of a circle with an area of 78.5 cm 2 . Determining Radius and Diameter. Ex 1) Find the radius of a circle with an area of 78.5 cm 2 . Solve by Trial and Error:. Determining Radius and Diameter.

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Determining Radius and Diameter

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  1. Determining Radius and Diameter

  2. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Determining Radius and Diameter

  3. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Determining Radius and Diameter

  4. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → Determining Radius and Diameter

  5. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 Determining Radius and Diameter

  6. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm Determining Radius and Diameter

  7. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Determining Radius and Diameter

  8. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Determining Radius and Diameter

  9. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Try r = 5 cm → Determining Radius and Diameter

  10. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Try r = 5 cm → A = π r2 Determining Radius and Diameter

  11. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Try r = 5 cm → A = π r2 = 3.14 x 5 cm x 5 cm Determining Radius and Diameter

  12. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Try r = 5 cm → A = π r2 = 3.14 x 5 cm x 5 cm = 78.5 cm2 Determining Radius and Diameter

  13. Ex 1) Find the radius of a circle with an area of 78.5 cm2. Solve by Trial and Error: Try r = 3 cm → A = π r2 = 3.14 x 3 cm x 3 cm = 28.26 cm2 Too low. Try r = 5 cm → A = π r2 = 3.14 x 5 cm x 5 cm = 78.5 cm2 That’s it. Determining Radius and Diameter

  14. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Determining Radius and Diameter

  15. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Determining Radius and Diameter

  16. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → Determining Radius and Diameter

  17. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr Determining Radius and Diameter

  18. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Determining Radius and Diameter

  19. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Determining Radius and Diameter

  20. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → Determining Radius and Diameter

  21. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → C = 2πr Determining Radius and Diameter

  22. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → C = 2πr = 2 x 3.14 x 4 cm = 25.12 cm Determining Radius and Diameter

  23. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → C = 2πr = 2 x 3.14 x 4 cm = 25.12 cm Too high. Determining Radius and Diameter

  24. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → C = 2πr = 2 x 3.14 x 4 cm = 25.12 cm Too high. But which is closer? Determining Radius and Diameter

  25. Ex 2) Find the radius, to the nearest cm, of a circle with a circumference of 20 cm. Solve by trial and error: Try r = 3 cm → C = 2πr = 2 x 3.14 x 3 cm = 18.84 cm Too low. Try r = 4 cm → C = 2πr = 2 x 3.14 x 4 cm = 25.12 cm Too high. But which is closer? 18.84 cm is closer to 20 cm, so the radius is approximately 3 cm. Determining Radius and Diameter

  26. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. Determining Radius and Diameter

  27. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. Solve by working backwards through the formula: Determining Radius and Diameter

  28. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. Solve by working backwards through the formula: We know that to go from radius to area, we must; Determining Radius and Diameter

  29. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. Solve by working backwards through the formula: We know that to go from radius to area, we must; - square the radius Determining Radius and Diameter

  30. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • - multiply by 3.14 Determining Radius and Diameter

  31. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • - multiply by 3.14 (A = πr2) Determining Radius and Diameter

  32. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • multiply by 3.14 (A = πr2) • So, to go from area to radius, we must do the opposite; Determining Radius and Diameter

  33. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • multiply by 3.14 (A = πr2) • So, to go from area to radius, we must do the opposite; • - divide by 3.14 Determining Radius and Diameter

  34. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • multiply by 3.14 (A = πr2) • So, to go from area to radius, we must do the opposite; • divide by 3.14 • - find the square root of r2 Determining Radius and Diameter

  35. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. • Solve by working backwards through the formula: • We know that to go from radius to area, we must; • square the radius • multiply by 3.14 (A = πr2) • So, to go from area to radius, we must do the opposite; • divide by 3.14 • - find the square root of r2 (r = √A / π) Determining Radius and Diameter

  36. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. r = √A / π Determining Radius and Diameter

  37. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. r = √A / π = √145.19 cm2 / 3.14 Determining Radius and Diameter

  38. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. r = √A / π = √145.19 cm2 / 3.14 = √46.23885. . . cm2 Determining Radius and Diameter

  39. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. r = √A / π = √145.19 cm2 / 3.14 = √46.23885. . . cm2 ≈ 6.8 cm Determining Radius and Diameter

  40. Ex 3) Determine the radius, to the nearest tenth of a centimetre, of a circle with an area of 145.19 cm2. r = √A / π = √145.19 cm2 / 3.14 = √46.23885. . . cm2 ≈ 6.8 cm The radius of the circle is 6.8 cm, rounded to the nearest tenth. Determining Radius and Diameter

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