FTCE General Knowledge Math Practice Test 2025 - Free Practice Questions and Study Guide

The formula for calculating the circumference of a circle can indeed be represented as C = 2πr. This formula directly relates the circumference (C) to the radius (r) of the circle, where π (pi) is a mathematical constant approximately equal to 3.14159.

In this formula, multiplying the radius by 2 gives the diameter of the circle, and then by multiplying by π, you effectively find the perimeter or boundary length of the circle. This relationship illustrates how the circumference is fundamentally tied to the circle's radius.

Other choices provided do not accurately calculate the circumference. For example, C = πd is correct too but uses the diameter instead of the radius. C = 2r does not involve π, which is essential in calculating the circumference. Finally, C = πr² represents the formula for the area of a circle, not the circumference. Thus, C = 2πr correctly conveys the relationship needed to find the circumference using the radius.