Objective

Find the circumference of circles

Vocabulary

Circle

The set of all points in a plane that are the same distance from a given point called the

center

Vocabulary

Center

The given point from which all points on a circle or sphere are the same distance

Vocabulary

Diameter

The distance across a circle through its center

Vocabulary

Radius

The distance from the center to any point on a circle

Vocabulary

Circumference

The distance around a circle (perimeter)

C = d

or

C =2r

Example 1 Find Circumference

Example 2 Find Circumference

PETS Find the circumference around the hamster’s running wheel shown below. Round to the nearest hundredth.

Determine if the radius or diameter has been given

C = 2 3.14 3

1/2

Write formula for circumference when radius is given

Bring down C = 2

Replace with 3.14

Replace r with 3

PETS Find the circumference around the hamster’s running wheel shown below. Round to the nearest hundredth.

Multiply the factors

C = 2 3.14 3

1/2

C = 18.84Note: If you use the key on the calculator you will get a slightly different answer, but just remember to round to the nearest hundredth

Add dimensional analysis

C = 18.84 inches

Answer: C = 18.84 inches

SWIMMING POOL A new children’s swimming pool is being built at the local recreation center. The pool is circular in shape with a diameter of 18 feet. Find the circumference of the pool. Round to the nearest hundredth.

Answer: 56.52 ft

1/2

Find the circumference of a circle with a diameter of 49 centimeters.

Answer: C = 153.86 cm

Write the formula for circumference of a circle using diameter

Bring down C = C = 3.14(49)

C = 153.86

2/2

Replace with 3.14

Replace d with 49

Multiply

Add dimensional analysis

C = 153.86 cm

Find the circumference of a circle with a radius of 35 feet.

Answer: C = 219.80 ft

*

2/2

Assignment

Lesson 6:9 Geometry: Circles and 4 - 23 All  Circumference