What is the formula for the circumference of a circle?

The formula for the circumference of a circle is correctly expressed as C = 2πr. This formula derives from the relationship between the radius of the circle and the distance around it. The symbol π (pi) represents the ratio of the circumference of any circle to its diameter, which is approximately 3.14.

In this formula, "C" stands for circumference, "r" represents the radius, and "d" (if referenced) would be the diameter, which is double the radius (d = 2r). Thus, when you multiply the radius by 2 and then by π, you are essentially calculating the entire distance around the circle. This formula is fundamental in both geometry and real-world applications, as it allows for the measurement of circular objects and paths.

Other options presented are not applicable for calculating circumference. For instance, C = πr² represents the area of a circle, and C = πd, although technically correct as it still relates circumference to diameter, is less frequently used than the more common 2πr formulation. Lastly, C = 4r does not correspond to any circle-related measurement and reflects a misunderstanding of circular dimensions.