Learn about the definition of pi in relation to a circle with this BBC Bitesize Maths article. For students between the ages of 11 and 14.

How to Solve for Radius in Excel. The radius of a circle or a sphere is the distance between the center and the edge. The radius can be used to calculate a circle's diameter, area and circumference.

Yes, this is essentially the same equation used to find the circumference of a circle if θ is measured in radians (which it should be).