What is the formula for calculating the circumference of a circle?

The formula for calculating the circumference of a circle is accurately represented by two primary equations: C = πd and C = 2πr. The option that states C = πd indicates that the circumference (C) is equal to pi (π) multiplied by the diameter (d) of the circle. This relationship arises because the diameter is twice the radius, and π is a constant that represents the ratio of the circumference to the diameter for any circle.

While the alternative formula, C = 2πr, is also valid, as it expresses the circumference in terms of the radius (r), both formulas ultimately yield the same result. Consequently, recognizing either equation as a means to calculate circumference is essential for understanding circular measurements.

In the other choices, C = πr² represents the formula for the area of a circle, rather than its circumference, and C = 2r is not a correct formula in the context of calculating either the circumference or area. Therefore, understanding the relationship between diameter, radius, and pi is crucial for using the wrong equations effectively.