A circle has a radius of 3 units. What is its circumference?

A circle has a radius of 3 units. What is its circumference?

• A. 3π
• B. 9π
• C. 12π
• D. 6π

Answer: (D)

Use the circumference formula C = 2πr (or C = πd). With a radius of 3, the circumference is C = 2π × 3 = 6π. You can check with the diameter since d = 2r = 6, and C = πd = 6π, which matches. The other numbers come from leaving out the factor of 2 or mixing up radius and diameter, which leads to incorrect results like 3π, 9π, or 12π.

Use the circumference formula C = 2πr (or C = πd). With a radius of 3, the circumference is C = 2π × 3 = 6π. You can check with the diameter since d = 2r = 6, and C = πd = 6π, which matches. The other numbers come from leaving out the factor of 2 or mixing up radius and diameter, which leads to incorrect results like 3π, 9π, or 12π.