- C – Circumference of a Circle
- A – Area of a Circle
- r – radius
- D – Diameter of a Circle
- P – center point

## Find the Area and Perimeter of the Circle

The area of a circle can be found in various ways, in general the known parameters are the radius or the diameter. Here are some examples of finding the area of a circle with known parameters.

Example of Calculating Area if you Know the Finger (r)

What is the area of the circle if you know the radius is 20 cm.

answers:

r=20 ; d = 2r = 40

A=π.r^{2} ; K = 2. πr atau 2.rd

A=3.14 * 20^{2 }= 1256 Cm

C=2*3.14*40 = 125.6

Example of Calculating Area if you know the Diameter (d)

What is the area and circumference of the circle if the diameter is 10 cm?

Answers:

d = 10; r = 10/2=5

A=π.r^{2} ; K = 2. πr atau 2.rd

A=3.14 * 5^{2 }= 79.5 Cm

C=2*3.14*10= 31.4 CM

Example of calculating area, radius and diameter if you know the circumference

What is the Area of a Circle if the circumference is 314 cm

Answers:

d = ?; r = ?

A=π.r^{2} ; K = 2. πr atau 2.rd

r = K/2.π

r=314/(2*3.14) = 50 cm

D= 50 * 2 = 100 cm

A=3.14*50^{2} = 7850 cm

Example of Calculating the circumference, radius and diameter if you know the area

What is the circumference of the circle if the area is 7850 cm

Answers:

A=400 ; d = ?; r = ? ; K=?

A=π.r^{2} ; K = 2. πr atau 2.rd

r = √ L/π = √ 7850/3.14 = 50 cm

D= 50*2 = 100cm

C=2*3.14*50 = 314cm