How to Calculate the Area of a Circle
What is the formula needed to calculate the area of a circle?
Area of a circle equals pi times the radius squared (A = πr2). Pi is a mathematical constant that represents the ratio of the circumference to the diameter of a circle. Pi is an irrational number, a number that never ends and cannot be represented as a fraction. Pi is approximately equal to 3.14159...
The radius of a circle is half of the diameter, which is a special chord that goes from one end of the circle through the middle to another end on the opposite side. Since the radius is equal to half of the diameter another representation of the area of the circle is equal to pi times the diameter divided by 2 squared (A = π*(d/2)2). Both of these formulas are equivalent (A = πr2 = π*(d/2)2).
Let's look at some examples.
1) What is the area of a circle whose radius is 5 inches?
A = πr2
A = π*(5 inches)2
A = 25π inches2
2) What is the area of a circle whose radius is 1 cm?
A = πr2
A = π*(1 cm)2
A = π cm2
3) What is the area of a circle whose diameter is 12 feet?
A = π*(d/2)2
A = π*(12/2 feet)2
A = π*(6 feet)2
A = 36π feet2
Published by Jeremy Ross
I am a recent graduate from the University of Rochester where I received a B.S. degree in mathematics. I am writing to help keep my sanity. View profile
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