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Learn how to find areas of circles, use formulas, and solve circle-related problems in this comprehensive math lesson. Includes step-by-step examples and practice exercises.

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  1. Transparency 3 Click the mouse button or press the Space Bar to display the answers.

  2. Splash Screen

  3. Example 3-1a Objective Find the areas of circles

  4. Example 3-1a Vocabulary Circumference The distance around a circle

  5. Example 3-1a Symbols Pi Approximately 3.14 You are to use the  key on the calculator

  6. Lesson 3 Contents Example 1Find Areas of Circles Example 2Find Area of Circles Example 3Use Area to Solve a Problem

  7. Example 3-1a Find the area of the circle to the nearest hundredth A =   (5 yd)2 Draw the circle and label the radius Write formula for area of circle Replace r with 5 yd 1/3

  8. Example 3-1a Find the area of the circle to the nearest hundredth Follow Order of Operations P E MD AS A =   (5 yd)2 A =   25 yd2 Must do exponents before multiplying Answer: A = 78.54 yd2 Find square of 5 yd Multiply by  1/3

  9. Example 3-1b Find the area of the circle to the nearest hundredth Answer: 50.27 cm2 1/3

  10. Example 3-2a Find the area of the circle to the nearest hundredth Draw the circle and label the diameter Remember: Diameter goes all the way across the circle and twice the radius Write formula for area of circle 2/3

  11. Example 3-2a Find the area of the circle to the nearest hundredth Since diameter is given must divide the diameter by 2 to find radius A =   (5.4 in)2 10.8  2 = 5.4 Replace r with 5.4 in 2/3

  12. Example 3-2a Find the area of the circle to the nearest hundredth Follow Order of Operations P E MD AS A =   (5.4 in)2 A =   29.18 in2 Must do exponents before multiplying Answer: Find square of 5.4 in A = 91.61 in2 Multiply by  2/3

  13. Example 3-2b Find the area of the circle to the nearest hundredth Answer: 124.69 m2 2/3

  14. Example 3-3a CRATERS The Chicxulub Crater in the Yucatan Peninsula, Mexico, was caused by a crashing asteroid or comet about 65 million years ago. If the diameter measures 300 kilometers, what is the area covered by the crater? Draw the circle and label the diameter 300 km Remember: Diameter goes all the way across the circle and twice the radius Write formula for area of circle 3/3

  15. Example 3-3a 300 km A =   (150 km)2 Since diameter is given must divide the diameter by 2 to find radius 300  2 = 150 Replace r with 150 km 3/3

  16. Example 3-3a 300 km A =   (150 km)2 Follow Order of Operations P E MD AS A =   22,500 km2 Must do exponents before multiplying Answer: Find square of 150 km A = 70,685.83 km2 Multiply by  3/3

  17. Example 3-3b SWIMMING POOL A new children’s circular swimming pool being built at a local recreation center has a diameter of 24 feet. How much area does the new pool cover? Answer: 452.39 ft2 3/3

  18. End of Lesson 3 Assignment

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