# Definition:Radius

Jump to navigation
Jump to search

## Disambiguation

This page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

**Radius** may refer to:

- Geometry:
- Radius of a Circle: a straight line segment whose endpoints are the center and the circumference of the circle.
- Radius of a Sphere: a straight line segment whose endpoints are the center and the surface of the sphere.

- Analytic Geometry:
- The radial coordinate of a point $P$ in a system of polar coordinates is also known as the
**radius**of $P$.

- The radial coordinate of a point $P$ in a system of polar coordinates is also known as the

- Topology and Metric Spaces:
- Radius of an $\epsilon$-Ball: In the open $\epsilon$-ball $B_\epsilon \left({x}\right)$ of the point $x$, the value $\epsilon$ is its radius.

- Analysis:
- Radius of Convergence: The distance from the endpoints to the midpoint of the interval on which a power series is convergent.

## Linguistic Note

The plural of **radius** is **radii**, pronounced ** ray-dee-eye**.

This irregular plural form stems from the Latin origin of the word **radius**, meaning **ray**.

The ugly incorrect form **radiuses** can apparently be found, but rarely in a mathematical context.