What is the formula used to calculate the circumference of a circle?

The correct choice for calculating the circumference of a circle is based on the relationship between the diameter and Pi. In mathematical terms, the circumference ((C)) of a circle can indeed be described using the diameter ((D)) as follows:

[ C = \pi \times D

]

This relationship shows that to find the circumference, you multiply the diameter of the circle by Pi, which is approximately 3.14. This formula is a foundational aspect of geometry concerning circles.

While there are other formulas mentioned here, the one that specifically calculates circumference in relation to diameter is the second one. For instance, the formula involving radius directly relates to circumference as (C = 2 \times \pi \times R) (where (R) is the radius), and it can be derived from the diameter since the diameter is twice the radius. The use of ( \pi \times R^2) pertains to calculating the area of a circle and does not apply to circumference at all. Thus, the correct choice emphasizes the direct calculation of circumference using diameter and is essential in solving problems involving circular geometry.