# What is the radius?

Most often the term "radius" is used ingeometry. It was first used by the French scientist P. Ramus in 1569, although the term was generally in use only at the end of the 17th century. Literally, from Latin, the radius is translated as "beam, wheel spoke".

Let's take a closer look at what is the radius in geometry.

## Radius is ...

A radius is a segment that connectscenter of a circle or sphere with any point on a circle or sphere. The length of this segment is also called the radius. Note also that the radius is half the diameter.

If you need to find the radius of the circumscribed circle, then you can use the formulas from the article How to find the radius of the circumscribed circle.

As for the radius of the inscribed circle, the algorithm for its calculation can be found in the article of our website. How to find the radius of the inscribed circle.

Another meaning is the term "radius" when wewe are talking about the radius vector. A radius vector is a vector that specifies the position of a point in space with respect to a pre-fixed point. This point is called the "origin".

The term "radius" can be used not onlyin a scientific context, in particular, experienced drivers can talk about the radius of the turn. In this case, the turning radius is the radius of the circumference, described by the outer point (as far from the center as possible) of the car.