How do you calculate the circumference of a circle?

The calculation of the circumference of a circle is based on the relationship between the radius or diameter of the circle and the mathematical constant pi (π). The correct formula for calculating circumference can be expressed in two ways depending on whether you use the radius or the diameter.

Using the radius, the circumference is calculated by multiplying 2 by π and by the radius (2πr). This is because the radius is half of the diameter, and when you double the radius, you essentially calculate the perimeter of the circle based on its circular nature.

Alternatively, if you are using the diameter, the circumference can also be calculated by multiplying π by the diameter (πd), since the diameter is twice the radius.

As to the other options, while π times the diameter is also a correct method to find circumference, the option that directly uses the radius in the form of 2πr is specifically suitable for situations where the radius is known, which solidifies its correctness in the context of this question.

The formula πr², on the other hand, is used to calculate the area of a circle, not its circumference. The expression "radius + π" does not relate to the concept of circumference at all, making it irrelevant in this context. Thus