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Circle Geometry and Calculations Lesson

Learn how to find the circumference and area of circles, understand key terms like radius and diameter, and practice using formulas for circle calculations.

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Circle Geometry and Calculations Lesson

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  1. Transparency 2 Click the mouse button or press the Space Bar to display the answers.

  2. Splash Screen

  3. Example 2-5e Objective Find the circumference and area of circles

  4. Example 2-5e Vocabulary Circle A set of all points in a plane that are the same distance from a given point called the center

  5. Example 2-5e Vocabulary Center The given point from which all points on a circle are the same distance

  6. Example 2-5e Vocabulary Radius The distance from the center of a circle to any point on the circle

  7. Example 2-5e Vocabulary Diameter The distance across a circle through its center

  8. Example 2-5e Vocabulary Circumference The distance around a circle

  9. Example 2-5e Vocabulary pi The ratio of the circumference of a circle to its diameter Pi = 3.14 

  10. Lesson 2 Contents Example 1Find the Circumferences of Circles Example 2Find the Circumferences of Circles Example 3Find the Areas of Circles Example 4Find the Areas of Circles

  11. Example 2-1a Find the circumference of the circle. Round to the nearest hundredth. Write formula for circumference Replace d with 5 C = 15.71 feet Multiply Add dimensional analysis Answer: C = 15.71 feet 1/4

  12. Example 2-1b Find the circumference of the circle. Round to the nearest hundredth. Answer: C = 21.98 inches 1/4

  13. Example 2-2a Find the circumference of the circle. Round to the nearest hundredth. C =   7.6 Write formula for circumference Replace d with 5 Answer: Remember: If given radius then double it for the diameter meters C = 23.86 D = 3.8  2 Multiply Add dimensional analysis 2/4

  14. Example 2-2b Find the circumference of the circle. Round to the nearest hundredth. Answer: C = 22.61 meters 2/4

  15. Example 2-3a Find the area of the circle. Round to the nearest hundredth. Write formula for area of a circle Replace r with 3 Follow Order of Operations P E MD AS Evaluate 32 3/4

  16. Example 2-3a Find the area of the circle. Round to the nearest hundredth. Multiply Add dimensional analysis Answer: yards2 A = 28.26 3/4

  17. Example 2-3b Find the area of the circle. Round to the nearest hundredth. Answer: A = 12.56 feet2 3/4

  18. Example 2-4a Find the area of the circle. Round to the nearest hundredth. Write formula for area of a circle Replace r with 5 Remember: If given the diameter, divide by 2 R = 10  2 4/4

  19. Example 2-4a Find the area of the circle. Round to the nearest hundredth. Follow Order of Operations P E MD AS Evaluate 52 Answer: Multiply inches2 A = 78.50 Add dimensional analysis 4/4

  20. Example 2-4b Find the area of the circle. Round to the nearest hundredth. Answer: 50.24 centimeters2 4/4

  21. End of Lesson 2 Assignment

  22. Example 2-5a POOLSThe Patels have a circular pool with a radius of 12 feet. They plan on installing a 4-foot-wide walkway around the pool. What will be the area of the walkway? To determine the area of the walkway, you must subtract the area of the pool from the area of the outer circle that includes the pool and the walkway. 5/5

  23. Replace r with 12 4 or 16. Evaluate Example 2-5b Area of Outer Circle Area of a circle A = 803.84 Multiply 5/5

  24. Evaluate Example 2-5c Area of Pool Area of a circle Replace r with 12. A = 452.16 Multiply 5/5

  25. Area of Walkway Area of Outer Circle – Area of Pool Example 2-5d 803.84 - 452.16 351.86 Answer: The area of the walkway is 351.86 feet2 5/5

  26. Example 2-5e * GARDENSThe Shoemakers have a circular pond with a radius of 4 feet. They plan on installing a 2-foot-wide walkway around the pond. What will be the area of the walkway? Answer: Area of walkway is 62.80 ft2 5/5

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