Which formula represents the relationship between the radius and the circumference of a circle?

The formula that illustrates the relationship between the radius and the circumference of a circle is expressed as C = 2πr. This means that the circumference (C) is equal to two times pi (π), which is approximately 3.14, multiplied by the radius (r) of the circle.

This formula stems from the geometric properties of circles. The radius is the distance from the center of the circle to its edge, and when you multiply this distance by 2π, you obtain the total distance around the circle's edge, which is the circumference. Understanding this relationship is crucial, as it allows for calculations involving circles based on their size.

The other formulas listed are related to circles but represent different relationships. For example, C = πr² is the formula for the area of the circle, and C = πd relates circumference to diameter, with the diameter being twice the radius. Meanwhile, C = r/2 does not accurately reflect any relationship within the context of circles.