Final answer:
The circumference of a circle is calculated using the formula C = πD, which is derived from the concept that the arc length over one full rotation equals the circumference, and π (pi) represents the ratio of that circumference to its diameter.
Step-by-step explanation:
The formula C = πD, where C represents the circumference of a circle and D is the diameter, is a fundamental concept in geometry, a branch of mathematics. When the radius (r) of a circle is rotated through a complete revolution (angle Δθ), the resulting arc length (As) becomes the circle's circumference. The diameter of the circle is twice the radius, so we can express the circumference also as C = 2πr where π (pi) is approximately 3.14159, the ratio of the circumference of any circle to its diameter. This understanding comes from ancient Greek mathematics and is still used today to calculate the distance around circular objects.