How to Find the Circumference of a Circle
The circumference or the perimeter of the circle can be found by the formula:
C = 2πr
where r is radius of the circle, π (pi number) is the mathematical constant ≈ 3.141592653589793
Example nr. 1:
x2 + y2 = 5 => x2 + y2 = (√5)2
r = √5 => C = 2πr = 2π√5 = 2√5π
C = 2√5π ≈ 2√5 * 3.141592653589793
Example nr. 2:
Let diameter of the circumference is D = 24, then find C - ?
C = 2πr = C = 2π
D2
= πD = 24πC = 24π
Example nr. 3:
Let C = 30π, then find D - ?
C = 2πr => 2πr = 30π
2r = 30
D = 30
Note: Don't forget that C = 2πr =>
Cr
= 2π = const for every circumference of a circle.