lesson 1 mi/vocab

• circle• center• radius• diameter• circumference• pi

• Find the circumference and area of circles.

Find the Circumferences of Circles

Find the circumference of the circle. Round to the nearest tenth.

Answer: The circumference is about 15.7 feet.

C = d Circumference of a circle

C = 5 Replace d with 5.

C = 5 This is the exact circumference.

Use a calculator to find 5. 5 15.70796327× ENTER=

A. AB. BC. CD. D

A B C D

0% 0%0%0%

A. 38.5 in.

B. 31.4 in.

C. 22.0 in.

D. 19.7 in.

Find the circumference of the circle. Round to the nearest tenth.

Find the Circumferences of Circles

Find the circumference of the circle. Round to the nearest tenth.

Answer: The circumference is about 23.9 meters.

C = 2r Circumference of a circle

C = 2 3.8 Replace r with 3.8.

C ≈ 23.9 Use a calculator.

1. A2. B3. C4. D

0%0%0%0%

A B C D

A. 9.4 m

B. 11.3 m

C. 18.5 m

D. 22.6 m

Find the circumference of the circle. Round to the nearest tenth.

Find the Areas of Circles

Find the area of the circle. Round to the nearest tenth.

Answer: The area is about 28.3 square yards.

A = r2 Area of a circle

A = 32 Replace r with 3.

A = 9 Evaluate 32.

A ≈ 28.3 Use a calculator.

1. A2. B3. C4. D

0%0%0%0%

A B C D

A. 12.6 ft2

B. 14.1 ft2

C. 15.3 ft2

D. 17.4 ft2

Find the area of the circle. Round to the nearest tenth.

Find the area of the circle. Round to the nearest tenth.

Answer: The area is about 78.5 square inches.

Find the Areas of Circles

A = r2 Area of a circle

A = 52 Replace r with half of 10 or 5.

A = 25 Evaluate 52.

A ≈ 78.5 Use a calculator.

A. AB. BC. CD. D

A B C D

0% 0%0%0%

A. 42.7 cm2

B. 50.3 cm2

C. 52.1 cm2

D. 54.6 cm2

Find the area of the circle. Round to the nearest tenth.

POOLS The Patels have a circular pool with a radius of 12 feet. They plan on installing a 4-foot-wide walkway around the pool. What will be the area of the walkway?

To determine the area of the walkway, you must subtract the area of the pool from the area of the outer circle that includes the pool and the walkway.

Area of Outer Circle

A = r2 Area of a circle

A = (16)2 Replace r with 12 + 4 or 16.

A = 256 Evaluate 162.

Area of Pool

A = r2 Area of a circle

A = 122 Replace r with 12.

A = 144 Evaluate 122.

Area of Walkway = Area of Outer Circle – Area of Pool

Answer: The area of the walkway is about 351.9 square feet.

≈ 256 – 144

≈ 351.9

A. AB. BC. CD. D

A B C D

0% 0%0%0%

A. 62.8 ft2

B. 84.3 ft2

C. 99.2 ft2

D. 113.1 ft2

POOLS The Shoemakers have a circular pond with a radius of 4 feet. They plan on installing a 2-foot-wide walkway around the pond. What will be the area of the walkway?