Contributed by:

Circumference of the circle or perimeter of the circle is the measurement of the boundary of the circle. The area of a circle is π multiplied by the square of the radius. The area of a circle(A) when the radius 'r' is given is πr^2. π is approx 3.14 or 22/7.

1.
Parts of a Circle

Area & Circumference

Area & Circumference

2.

3.
RADIUS = ½ OF DIAMETER

If the radius is 5 cm, what is the diameter? 10

If the diameter is 32 ft, what is the radius? cm

16 ft

58 cm 78 cm

What is the What is the

diameter? 116 radius? 39

cm cm

If the radius is 5 cm, what is the diameter? 10

If the diameter is 32 ft, what is the radius? cm

16 ft

58 cm 78 cm

What is the What is the

diameter? 116 radius? 39

cm cm

4.
CIRCUMFERENCE OF A CIRCLE

Formula is C = 2r (2 x Pi x Radius)

or

C = d (Pi x Diameter)

Remember… = 3.14 (approximately)

*You can use either formula

depending on what they give you in

the original problem

Formula is C = 2r (2 x Pi x Radius)

or

C = d (Pi x Diameter)

Remember… = 3.14 (approximately)

*You can use either formula

depending on what they give you in

the original problem

5.
The circumference of a circle

Use π = 3.14 to find the circumference of the following circles:

C = πd 9m C = 2πr

4 cm

= 3.14 × 4 = 2 × 3.14 × 9

= 12.56 cm = 56.52 m

C = πd C = 2πr

58 cm

23 mm = 3.14 × 23 = 2 × 3.14 × 58

= 72.22 mm = 364.24 cm

Use π = 3.14 to find the circumference of the following circles:

C = πd 9m C = 2πr

4 cm

= 3.14 × 4 = 2 × 3.14 × 9

= 12.56 cm = 56.52 m

C = πd C = 2πr

58 cm

23 mm = 3.14 × 23 = 2 × 3.14 × 58

= 72.22 mm = 364.24 cm

6.
AREA OF A CIRCLE

Formula is A = r2 (Pi x Radius Squared)

radius

Formula is A = r2 (Pi x Radius Squared)

radius

7.
The area of a circle

Use π = 3.14 to find the area of the following circles:

2 cm A = πr2 A = πr2

10 m

= 3.14 × 2 2

= 3.14 × 52

= 12.56 cm2 = 78.5 m2

A = πr2 A = πr2

78 cm

23 mm = 3.14 × 232 = 3.14 × 392

= 1661.06 mm2 = 4775.94 cm2

Use π = 3.14 to find the area of the following circles:

2 cm A = πr2 A = πr2

10 m

= 3.14 × 2 2

= 3.14 × 52

= 12.56 cm2 = 78.5 m2

A = πr2 A = πr2

78 cm

23 mm = 3.14 × 232 = 3.14 × 392

= 1661.06 mm2 = 4775.94 cm2

8.
Finding the Radius or Diameter

• Circumference • Area

C = 5 in. A = 8.9 m2

Calculate the diameter… Calculate the radius…

• Circumference • Area

C = 5 in. A = 8.9 m2

Calculate the diameter… Calculate the radius…