Assessment and Learning in Knowledge Spaces (ALEKS) Basic Math Placement Practice Test

How is the circumference of a circle determined?

1. A = pi x r^2

2. C = pi x d

3. C = 2 x pi x r

4. P = side + side

The correct answer is: C = 2 x pi x r

The circumference of a circle is the total distance around the circle. It can be calculated using the formula that relates the radius and pi, specifically \(C = 2 \times \pi \times r\). In this formula, "C" represents the circumference, "r" stands for the radius of the circle, and pi (π) is a mathematical constant approximately equal to 3.14. This formula effectively shows that the circumference is proportional to the radius, doubling the radius to get the diameter and then multiplying by pi to account for the circle's geometric properties. While pi is also used in the formula relating circumference to diameter, expressed as \(C = \pi \times d\), the choice that directly relates to the radius and is commonly used is indeed \(C = 2 \times \pi \times r\). This formula clearly illustrates the connection between the radius and the circumference, making it a fundamental concept in understanding circular measurements.