Do Now Evaluate. 1. 6  42 2. 5.6  23 96 Simplify each expression. 44.8 n + 2 5n + 5

4/15/2015 9-2 D Area of Circles

Example 1 Estimate the area of the circle. Use 3 to approximate . A = r2 A ≈ 3 • 202 A ≈ 3 • 400 A ≈ 1,200 m2

Estimate the area of the circle. Use 3 to approximate . Example 2 Estimate the area of the circle. Use 3 to approximate . A = r2 r = d ÷ 2 r = 28 ÷ 2 r = 14 A ≈ 3 • 142 A ≈ 3 • 196 A ≈ 588 m2

Find the area of the circle. Use for . 22 7 Example 3 Find the area of the circle. Use for . 22 7 A = r2 r = d ÷ 2 r = 8 ÷ 2 = 4 A  • (4)2 22 7 A  • 16  22 7 __ 352 7 2 7 A  50 ft2

Find the area of the circle. Use for . 22 7 Example 4 Find the area of the circle. Use for . 22 7 A = r2 A  • 72 22 7 A  • 49 22 7 __ 7 1 A  154 cm2

Example 5 A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for . A = r2 18 in. A  3.14 • 182 A  3.14 • 324 A  1,017.36 in.2

Example 6 Find the area of the circle. Use 3.14 for . Estimate 3 × 4 × 4 = 48 A = r2 A ≈ 3.14 ● 42 A ≈ 3.14 ● 16 A ≈ 50.24 The area of the circle is approximately 50.24 square centimeters. Check for Reasonableness 50.24 ≈ 48 

Example 7 Find the area of the fountain shown. Use 3.14 for . Round to the nearest tenth if necessary. Estimate 3 × 3 × 3 = 27 A = r2 A ≈ 3.14 ● 2.62 A ≈ 3.14 ● 6.76 A ≈ 21.2 The area is approximately 21.2 square meters.

Example 8 Find the area of the semicircle. Use 3.14 for . Round to the nearest tenth if necessary. Replace r with 4.5

A ≈ 0.5(3.14)(4.5)2 Use 3.14 for . A ≈ 0.5(3.14)(20.25) 4.52 = 4.5 ● 4.5 = 20.25 A ≈ 31.8 Simplify. The area of the semicircle is approximately 31.8 square centimeters.

Exit Ticket Estimate the area of each circle. 1. 2. 27 km2 1,200 yd2 1. 2. 27 km2 1,200 yd2 13

Find the area of each circle. Use for . 22 3. 4. 7 3. 4. 7 4.53 cm2 1.54 m2 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 14

1. Estimate the area of the circle. Use 3 for . A. 48 km2 B. 46 km2 C. 44 km2 D. 42 km2 4 km

2. Estimate the area of the circle. Use 3 for . A. 772 yd2 B. 872 yd2 C. 972 yd2 D. 992 yd2 36 yd

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

4. A circular table has a diameter of 8 feet 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

Homework Pg. 553 #1-20 All Study for Ch. 9 Quiz II