The correct formula to find the circumference of a circle when the radius is given is:
C = 2πr
However, this specific option is not listed among your responses. From your responses, the closest correct option is not present, but it's important to note that:
- C = πr is incorrect (it represents the area of a circle).
- C = πr² is for the area, not circumference.
- C = π²d is also incorrect.
- C = π2r is a miswritten version and could be intended for circumference if it's interpreted as "C = 2πr."
To summarize: The correct formula for the circumference is C = 2πr.