Question

which formula is used to calculate the circumference of a circle? a. $a = 2\pi r^{2}$ b. $c = \pi d$ c. $c = 2r$ d. $a = \pi r^{2}$

Explanation:

Step1: Analyze each option

• Option a: $A = 2\pi r^{2}$ is not a standard formula for circumference. It is not a correct formula for circle - related basic properties (the formula for the surface area of a sphere is \(S = 4\pi r^{2}\), and for a circle, area \(A=\pi r^{2}\)).
• Option b: The circumference of a circle \(C\) can be calculated using the formula \(C=\pi d\), where \(d\) is the diameter of the circle (\(d = 2r\), \(r\) is the radius).
• Option c: \(C = 2r\) is incorrect. The correct formula related to radius for circumference is \(C = 2\pi r\), and \(2r\) is the formula for the diameter (\(d\)) of a circle.
• Option d: \(A=\pi r^{2}\) is the formula for the area of a circle, not the circumference.

Answer:

B. \(C=\pi d\)