Question

question 4 of 44
which of the following formulas is used to find the circumference of a circle?

a. ( c = pi r^2 )

b. ( c = 2pi r )

c. ( c = 2pi d )

d. ( c = pi d^2 )

Explanation:

To determine the formula for the circumference of a circle, we recall the basic concepts:

• The formula for the area of a circle is \( A=\pi r^{2} \), so option A is for area, not circumference.
• The circumference of a circle can be calculated using the radius \( r \) as \( C = 2\pi r \) (since the diameter \( d=2r \), we can also write it as \( C=\pi d \)).
• Option C has an incorrect coefficient (it should be \( \pi d \) or \( 2\pi r \), not \( 2\pi d \)).
• Option D is incorrect as it resembles a wrong formula for area or circumference (mixing diameter squared which is not part of the circumference formula).

So the correct formula for the circumference of a circle is \( C = 2\pi r \) (option B).

Answer:

B. \( C = 2\pi r \)