What is the formula for the circumference of a circle in terms of diameter?

The formula for the circumference of a circle is expressed in terms of its diameter as C = π × d, where C represents the circumference and d represents the diameter. This relationship establishes that the circumference is directly proportional to the diameter, with π (approximately 3.14) as the constant of proportionality.

This formula reflects the geometric property of circles, where the circumference is the total distance around the circle. Therefore, multiplying the diameter by π gives the correct measure of this distance.

The other choices present different calculations that do not define the circumference correctly. For instance, the option that suggests multiplying the diameter by 2π implies a different relationship (specifically, this actually describes the circumference in terms of the radius, where r = d/2), and another option divides the diameter instead of creating an appropriate relationship. Recognizing the significance of π in the context of circle measurements aids in understanding why option A is the accurate choice for the formula of circumference in terms of diameter.