Over Lesson 11–6

You have already found the perimeter of rectangles. (Lesson 5–1)

• Find the circumference of circles.

• Solve problems involving circumference.

1. Use the ruler to measure the diameter of the cylinder (in inches) and record it in your notebook.

2. Use the tape measure to estimate the circumference (in inches). Make sure you use the yellow side!

3. What is the relationship between the circumference and the diameter?

Circumference Activity

• Circumference - the distance around the circle

• (pi) – the ratio of the circumference to the diameter

Find the Circumference of a Circle

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

C = d Circumference of a circle

= ● 12 Replace d with 12.

= 12 Simplify. This is the exact circumference.

Answer: The circumference is about 37.7 inches.

To estimate the circumference, use a calculator.

ENTER× 2nd12 [ ] 37.69911184

A. 12 ft

B. 12.6 ft

C. 25.1 ft

D. 50.3 ft

Find the circumference of the circle to the nearest tenth.

Find the Circumference of a Circle

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

Answer: The circumference is about 44.6 meters.

C = d Circumference of a circle

= ● 14.2 Replace d with 14.2.

44.6 Simplify. Use a calculator.

r = 7.1 m

d = 7.1 x 2 = 14.2 m

A. 5.0 cm

B. 8.0 cm

C. 10.1 cm

D. 32.2 cm

Find the circumference of the circle to the nearest tenth.