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Area of Circles

Area of Circles. #35. VOCABULARY. Circle. VOCABULARY. r = 28 ÷ 2. r = 14. A ≈ 3 • 14 2. A ≈ 3 • 196. A ≈ 588 ft 2. Example 1 : Estimating the Area of a Circle Estimate the area of the circle. Use 3 to approximate  . Write the formula for area. A =  r 2.

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Area of Circles

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  1. Area of Circles #35

  2. VOCABULARY • Circle

  3. VOCABULARY

  4. r = 28 ÷ 2 r = 14 A ≈3 • 142 A ≈3 • 196 A ≈588 ft2 Example 1: Estimating the Area of a Circle Estimate the area of the circle. Use 3 to approximate . Write the formula for area. A = r2 The length of the radius is half the length of the diameter. r = d ÷ 2 Divide. Replace  with 3 and r with 14. Use the order of operations. Multiply.

  5. Example 2 Estimate the area of the circle. Use 3 to approximate . 20 m 2  A = r2 ≈ 3 • 102 = 300 m

  6. r = d ÷2 r = 14÷2 = 7 22 22 __ A • (7)2 Replace  with and r with 7. 7 7 22 __ A • 49 7 Example 3: Using the Formula for the Area of a Circle Find the area of the circle. Use for . 22 7 Write the formula to find the area. A = r2 The length of the diameter is twice the length of the radius. Simplify. A 154 ft2

  7. Example 4 Find the area of the circle. Use for . 22 7 3 m A =  r2 2 227 32  114 2 7m 

  8. A 3.14 • 182 A 3.14 • 324 A 1,017.36 in2 Example 5: Application A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for . Write the formula for area. A = r2 18 in. Replace  with 3.14 and r with 18. Use the order of operations. Multiply.

  9. Example 6 The figure shows the dimensions of a standard compact disc. What is the area of the hole in a compact disc? Use 3.14 for and round to the nearest tenth. π

  10. Example 6Continued d = 1.5 cm; r = 0.75 cm A = πr ≈ (3.14)(0.7 5) ≈ 1.766 The area of the hole is about 1.8 cm . 2 2 2

  11. Example 7 A circular living room has a diameter of 16 ft. Carpeting for the room costs $2.25 per square foot. How much does it cost to put wall-to-wall carpeting in the room? Use 3.14 for π. 2 2 A = πr ≈ (3.14) (8) ≈ 201 201 × 2.25 = 452.25 It costs $452.25 to carpet the room.

  12. VOCABULARY • Circumference C = 2 Π r or C =Π d

  13. Example 8 • The diameter of a tire is 24. What is the circumference of the tire?

  14. Example 9 • The radius of the circular bottle cap is 2. What is the circumference?

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