Which expression represents the circumference of a circle in terms of its radius?

Which expression represents the circumference of a circle in terms of its radius?

• A. C = π d
• B. C = 2πr
• C. C = π r^2
• D. C = r^2

Answer: (D)

The circumference of a circle is the distance around it, and it relates to the radius through the constant pi. The standard formula using the radius is C = 2πr. This comes from the more general C = πd, since the diameter is twice the radius (d = 2r). Substituting gives C = π(2r) = 2πr. Remember, πr^2 is the area of a circle, not its circumference, and r^2 has no direct meaning as a circumference. So the expression in terms of the radius is C = 2πr.

The circumference of a circle is the distance around it, and it relates to the radius through the constant pi. The standard formula using the radius is C = 2πr. This comes from the more general C = πd, since the diameter is twice the radius (d = 2r). Substituting gives C = π(2r) = 2πr. Remember, πr^2 is the area of a circle, not its circumference, and r^2 has no direct meaning as a circumference. So the expression in terms of the radius is C = 2πr.