Radius

of a circle

A segment joining a point of the circle (or sphere) to the centre. The length of this segment is also called the radius.

Comments

For the radius of curvature of curves, surfaces and higher-dimensional differential-geometric objects, cf. e.g. Curvature and Differential geometry.

References

[a1]	M. Berger, "Geometry" , I , Springer (1987)
[a2]	H.S.M. Coxeter, "Introduction to geometry" , Wiley (1963)