Circumference
This article is a stub. Help us out by expanding it.
Circumference is essentially a synonym for perimeter: for a given closed curve in the plane, it is the distance one travels in a complete circuit of the curve. The term circumference is most frequently used to refer to the distance around a circle, though it may refer to the distance around any smooth curve, while the term perimeter is typically reserved for polygons and other non curving shapes.
Formulas
In a circle of radius and diameter , the circumference is given by
Indeed, the constant (pi) was originally defined to be the ratio of the circumference of a circle to the length of its diameter.
There is, however, no algebraic formula for the circumference of an ellipse (without integrals). Several approximations exist, such as this one:by Ramanujan.