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10-5

Area of Circles. 10-5. Course 1. Warm Up. Problem of the Day. Lesson Presentation. Area of Circles. 10-5. Course 1. Warm Up Evaluate. 1. 6  4 2 2. 5.6  2 3 Simplify each expression. 3. 6 + n – 4 4. 5( n + 1). 96. 44.8. n + 2. 5 n + 5. Area of Circles. 10-5.

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10-5

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  1. Area of Circles 10-5 Course 1 Warm Up Problem of the Day Lesson Presentation

  2. Area of Circles 10-5 Course 1 Warm Up Evaluate. 1. 6  42 2. 5.6  23 Simplify each expression. 3. 6 + n – 4 4. 5(n + 1) 96 44.8 n + 2 5n + 5

  3. Area of Circles 10-5 Course 1 Problem of the Day What is the area of a right triangle with legs measuring 31 in. and 21 in.? 325.5 in2

  4. Area of Circles 10-5 Course 1 Learn to find the area of a circle.

  5. Area of Circles 10-5 tttttttttttt Course 1

  6. Area of Circles 10-5 19.7 m A ≈ 3 • 202 A ≈ 1200 m2 A ≈ 3 • 400 Course 1 Additional Example 1A: Estimating the Area of a Circle Estimate the area of the circle. Use 3 to approximate pi. Write the formula for area. A = r2 Replace  with 3 and r with 20. Use the order of operations. Multiply.

  7. Area of Circles 10-5 r = 28 ÷ 2 A ≈3 • 142 A ≈3 • 196 r = 14 A ≈588 m2 Course 1 Additional Example 1B: Estimating the Area of a Circle Estimate the area of the circle. Use 3 to approximate pi. Write the formula for area. A = r2 The length of the radius is half the length of the diameter. r = d ÷ 2 28 m Divide. Replace  with 3 and r with 14. Use the order of operations. Multiply.

  8. Area of Circles 10-5 24.8 m A ≈ 3 • 252 A ≈ 1875 m2 A ≈ 3 • 625 Course 1 Check It Out: Example 1A Estimate the area of the circle. Use 3 to approximate pi. Write the formula for area. A = r2 Replace  with 3 and r with 25. Use the order of operations. Multiply.

  9. Area of Circles 10-5 r = 20 ÷ 2 A ≈3 • 102 A ≈3 • 100 A ≈300 m2 r = 10 Course 1 Check It Out: Example 1B Estimate the area of the circle. Use 3 to approximate pi. A = r2 Write the formula for area. The length of the radius is half the length of the diameter. r = d ÷ 2 20 m Divide. Replace  with 3 and r with 10. Use the order of operations. Multiply.

  10. Area of Circles 10-5 352 7 22 A • (4)2 Replace  with and r with 4. 7 22 22 __ __ A  • 16  r = 8 ÷ 2 = 4 r = d ÷ 2 7 7 Course 1 Additional Example 2A: Using the Formula for the Area of a Circle Find the area of the circle. Use for pi. 22 7 8 ft Write the formula to find the area. A = r2 The length of the diameter is twice the length of the radius. Use the order of operations. Divide. A 50.29 ft2

  11. Area of Circles 10-5 22 A •72 Replace  with and r with 7. 7 22 22 __ __ A  • 49 7 7 Course 1 Additional Example 2B: Using the Formula for the Area of a Circle Find the area of the circle. Use for pi. 22 7 Write the formula to find the area. A = r2 7 Use the GCF to simplify. 1 Multiply. A 154 cm2

  12. Area of Circles 10-5 22 A  • 142 Replace  with and r with 14. 7 22 22 __ __ A  • 196 r = 28 ÷ 2 = 14 r = d ÷ 2 7 7 Course 1 Check It Out: Example 2A Find the area of the circle. Use for pi. 22 7 28 cm A = r2 Write the formula to find the area. The length of the diameter is twice the length of the radius. 28 Use the GCF to simplify. 1 Multiply. A 616 cm2

  13. Area of Circles 10-5 22 A •72 Replace  with and r with 7. 7 22 22 __ __ A  • 49 7 7 Course 1 Check It Out: Example 2B Find the area of the circle. Use for pi. 22 7 7 cm Write the formula to find the area. A = r2 7 Use the GCF to simplify. 1 Multiply. A 154 cm2

  14. Area of Circles 10-5 A 3.14 • 182 A 3.14 • 324 A 1,017.36 in.2 Course 1 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 pi. Write the formula for area. A = r2 18 in. Replace  with 3.14 and r with 18. Use the order of operations. Multiply.

  15. Area of Circles 10-5 Course 1 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 pi. Check 18 in. Use 3 as an estimate for. The area, r2, is approximately 3 • 182 = 3 • 324 = 972, so the answer is reasonable.

  16. Area of Circles 10-5 r = 18 ÷ 2 A 3.14 • 92 A 254.34 m2 A 3.14 • 81 r = 9 Course 1 Check It Out: Example 3 A cymbal has a diameter of 18 in. Find its area. Use 3.14 for pi. 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.

  17. Area of Circles 10-5 Course 1 Check It Out: Example 3 Continued A drum head has a radius of 18 in. Find its area. Use 3.14 for pi. Check 18 m Use 3 as an estimate for. The area, r2, is approximately 3 • 92 = 3 • 81 = 243, so the answer is reasonable.

  18. Area of Circles 10-5 Course 1 Insert Lesson Title Here Lesson Quiz: Part I Estimate the area of each circle. 1.2. 27 km2 1200 yd2 3 km 38 yd

  19. Area of Circles 10-5 Course 1 Insert Lesson Title Here Lesson Quiz: Part II Find the area of each circle. Use for pi. 22 3.4. 7 0.7 m 2.4 cm 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 pi. 28.26 in2

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