Evaluate.1. 6 42

2. 5.6 23

Simplify each expression.3. 6 + n – 44. 5(n + 1)

9644.8

n + 25n + 5

Do Now

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

Example 1Estimate the area of the circle. Use 3 to approximate .

A ≈ 3 • 202

A ≈ 1,200 m2

A = r2

A ≈ 3 • 400

Example 2Estimate the area of the circle. Use 3 to approximate .

r = 28 ÷ 2

A ≈ 3 • 142

A = r2

r = 14

r = d ÷ 2

A ≈ 3 • 196A ≈ 588 m2

Example 3Find the area of the circle. Use for .

A = r2

r = d ÷ 2r = 8 ÷ 2 = 4

A • 16 22 7 __

A 50 ft2

22 7

A • (4)222 7

352 7

2 7

Example 4Find the area of the circle. Use for .

A = r2

A • 4922 7 __ 7

A 154 cm2

22 7

A • 7222 7

1

Example 5A drum head has a radius of 18 in. Find the area of the material covering the drum head. use 3.14 for .

A 3.14 • 182

18 in.A = r2

A 3.14 • 324

A 1,017.36 in.2

Example 6Find the area of the circle.Use 3.14 for .Estimate 3 × 4 × 4 = 48A = 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 7Find the area of the fountain shown. Use 3.14 for . Round to the nearest tenth if necessary.

Estimate 3 × 3 × 3 = 27A = r2 A ≈ 3.14 ● 2.62 A ≈ 3.14 ● 6.76 A ≈ 21.2

The area is approximately 21.2 square meters.

Example 8Find the area of the semicircle. Use 3.14 for . Round to the nearest tenth if necessary.

Replace r with 4.5

The area of the semicircle is approximately 31.8 square centimeters.

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.

Estimate the area of each circle.

1. 2.

27 km21,200 yd2

Exit Ticket

3. 4.

4.53 cm2 1.54 m2

Find the area of each circle. Use for .22 7

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

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. 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