Objective: Find the circumference and area of circles

Circle – Label The parts

Radius

Diameter

Circumference: C=2 rC=2 r

• Circumference is the length of the distance AROUND the circle

• Take 2 times the radius and pi

Circumference: C=2∏r

• Find the circumference of a circle with radius 5.

• Find the circumference of a circle with diameter 10.C r

C

C

C

C inches

2

2

1 0

1 0 3 1 4

3 1 4

(5)

( . )

.

5 in.C rorC d

C

C

C

C inches

2

1 0

1 0

1 0 3 1 4

3 1 4

( )

( . )

.

10 in.

Circumference

• Find the circumference of a circle with radius 2.

• Find the circumference of a circle with diameter 8.

C r 2

Area of a Circle

• AreaArea of a circle is the amount of space the circle covers.

A r 2

Area of a Circle

• Find the area of a circle with radius 9.

A r 2

A r

A

A

A

A

2

29

8 1

8 1 3 1 4

2 5 4 3 4

( )

( . )

.

9 feet

Find the area of the circles below. Use 3.14. 1) 2)

6 in.

2A r2A (6)

A 36A 36 A 36 (3.14)

2A 113.04 in

16 m

2A r2A (16)

A 256A (3.14) 256

2A 803.84 in

Area of a Circle

• Find the area of a circle with radius 5.

A r 2

Area of a Circle

• Find the area of a circle with diameter 24.

A r 2

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Problem #1Problem #1

What is the formula for circumference?

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Problem #2Problem #2• Find the circumference.

4

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Problem #3Problem #3

What is the formula for area of a circle?

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Problem #4Problem #4• Find the area.

20