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Learn to find the area of a circle .

Learn to find the area of a circle. A  3.14 • 18 2. A  3.14 • 324. A  1,017.36 in. 2. Additional Example 3: 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 =  r 2. 18 in.

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Learn to find the area of a circle .

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  1. Learn to find the area of a circle.

  2. A 3.14 • 182 A 3.14 • 324 A 1,017.36 in.2 Additional Example 3: 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.

  3. Additional Example 3 Continued A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for . Check 18 in. Use 3 as an estimate for. The area, r2, is approximately 3 • 182 = 3 • 324 = 972, so the answer is reasonable.

  4. r = 18 ÷ 2 r = 9 A 3.14 • 92 A 3.14 • 81 A 254.34 m2 Check It Out: Example 3 A cymbal has a diameter of 18 in. Find its area. Use 3.14 for . A = r2 Write the formula for area. The length of the radius is half the length of the diameter. r = d ÷ 2 18 m Divide. Replace  with 3.14 and r with 9. Use the order of operations. Multiply.

  5. Check It Out: Example 3 Continued A drum head has a radius of 18 in. Find its area. Use 3.14 for . Check 18 m Use 3 as an estimate for. The area, r2, is approximately 3 • 92 = 3 • 81 = 243, so the answer is reasonable.

  6. Lesson Quiz: Part I Estimate the area of each circle. 1.2. 1,200 yd2 27 km2

  7. Lesson Quiz: Part II Find the area of each circle. Use 3.14 for . 3.4. 1.54 m2 4.53 cm2 5. A coater has a diameter of 6 inches. Find the area of the largest cup the coaster can hold. Use 3.14 for . 28.26 in2

  8. Lesson Quiz for Student Response Systems • 1. Estimate the area of the circle. Use 3 for . • A. 48 km2 • B. 46 km2 • C. 44 km2 • D. 42 km2 4 km

  9. Lesson Quiz for Student Response Systems • 2. Estimate the area of the circle. Use 3 for . • A. 772 yd2 • B. 872 yd2 • C. 972 yd2 • D. 992 yd2 36 yd

  10. Lesson Quiz for Student Response Systems • 3. Estimate the area of the circle. Use 3 for . • A. 36.75 cm2 • B. 21 cm2 • C. 10.5 cm2 • D. 9.19 cm2 3.5 cm

  11. Lesson Quiz for Student Response Systems • 4. A circular table has a diameter of 8 feet. Identify the area of the table cloth needed to cover the table. Use 3.14 for . • A. 25.12 ft2 • B. 37.68 ft2 • C. 40.82 ft2 • D. 50.24 ft2

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