35 VOCABULARY Circle VOCABULARY Example 1 Estimating the
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VOCABULARY *Circle
VOCABULARY
Example 1: Estimating the Area of a Circle Estimate the area of the circle. Use 3 to approximate . A = r 2 Write the formula for area. r=d÷ 2 The length of the radius is half the length of the diameter. r = 28 ÷ 2 r = 14 Divide. A ≈ 3 • 142 Replace with 3 and r with 14. A ≈ 3 • 196 Use the order of operations. A ≈ 588 ft 2 Multiply.
Example 2 Estimate the area of the circle. Use 3 to approximate . 20 m A = r 2 ≈ 3 • 102 = 300 m 2
Example 3: Using the Formula for the Area of a Circle Find the area of the circle. Use 22 for . 7 A = r 2 r=d÷ 2 r = 14 ÷ 2 = 7 A A 22 • 7 22 __ • 7 Write the formula to find the area. The length of the diameter is twice the length of the radius. (7)2 __ and r with 7. Replace with 22 49 Simplify. A 154 ft 2 7
Example 4 Find the area of the circle. Use 22 for . 7 3 m A = r 2 22 7 7 1 14 3 2 2 m 2
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 . A = r 2 Write the formula for area. A 3. 14 • 182 Replace with 3. 14 and r with 18. A 3. 14 • 324 Use the order of operations. A 1, 017. 36 in 2 Multiply. 18 in.
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 π and round to the nearest tenth.
Example 6 Continued d = 1. 5 cm; r = 0. 75 cm 2 A = πr 2 ≈ (3. 14)(0. 7 5) ≈ 1. 766 The area of the hole is about 1. 8 cm 2.
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 × 2. 25 = 452. 25 It costs $452. 25 to carpet the room.
VOCABULARY *Circumference C=2Πr or C=Πd
Example 8 *The diameter of a tire is 24. What is the circumference of the tire?
Example 9 *The radius of the circular bottle cap is 2. What is the circumference?
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