# Radius

**radiiradialradiallycurve radiirradial headradial vectorsegmentsize**

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.wikipedia

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### Circle

**circularcircles360 degrees**

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.

The distance between any point of the circle and the centre is called the radius.

### Sphere

**sphericalhemisphereglobose**

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.

is the radius of the ball, which is made up from all points with a distance less than (or, for a closed ball, less than or equal to)

### Diameter

**Ddiameters⌀**

By extension, the diameter d is defined as twice the radius:

In this sense one speaks of the diameter rather than a diameter (which refers to the line segment itself), because all diameters of a circle or sphere have the same length, this being twice the radius r.

### Perimeter

**Perimeter lengthperimeter of the polygon**

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The radius of the circle with perimeter (circumference) C is

The perimeter of a circle, often called the circumference, is proportional to its diameter and its radius.

### Line segment

**segmentline segmentssegments**

In classical geometry, a radius of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length.

Any chord in a circle which has no longer chord is called a diameter, and any segment connecting the circle's center (the midpoint of a diameter) to a point on the circle is called a radius.

### Variable (mathematics)

**variablesvariableunknown**

The typical abbreviation and mathematical variable name for radius is r.

### Angle

**acute angleobtuse angleoblique**

The polar coordinate system is a two-dimensional coordinate system in which each point on a plane is determined by a distance from a fixed point and an angle from a fixed direction.

This measure is the ratio of the length of a circular arc to its radius.

### Circumference

**circumferentialgirthcircumferential line**

The radius of the circle with perimeter (circumference) C is

Or, equivalently, as the ratio of the circumference to twice the radius.

### Bend radius

**Minimum bend radiusbend radiiBends**

Bend radius, which is measured to the inside curvature, is the minimum radius one can bend a pipe, tube, sheet, cable or hose without kinking it, damaging it, or shortening its life.

### Radius of curvature

**radii of curvaturecurve radiusradius**

For a curve, it equals the radius of the circular arc which best approximates the curve at that point.

### Radius of gyration

**least radius of gyrationradii of gyration**

Mathematically the radius of gyration is the root mean square distance of the object's parts from either its center of mass or a given axis, depending on the relevant application.

### Area

**surface areaArea (geometry)area formula**

The radius of a circle with area

For a circle, the ratio of the area to the circumference (the term for the perimeter of a circle) equals half the radius r.

### Semidiameter

**semi-diameter**

The semi-diameter of a sphere, circle, or interval is the same thing as its radius — namely, any line segment from the center to its boundary.

### Geometry

**geometricgeometricalgeometries**

### Centre (geometry)

**centercentrecenters**

### Latin

**Latin languageLat.la**

The name comes from the Latin radius, meaning ray but also the spoke of a chariot wheel.

### Circumscribed circle

**circumcirclecircumcentercircumradius**

If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere.

### Circumscribed sphere

**circumspherecircumradiusvertex radius**

If an object does not have a center, the term may refer to its circumradius, the radius of its circumscribed circle or circumscribed sphere.

### Incircle and excircles of a triangle

**incircleinradiusinscribed circle**

The inradius of a geometric figure is usually the radius of the largest circle or sphere contained in it.

### Regular polygon

**regularregular polygons30-gon**

For regular polygons, the radius is the same as its circumradius.

### Apothem

**distance from its center to its sides**

The inradius of a regular polygon is also called apothem.

### Graph theory

**graphgraphsgraph-theoretic**

In graph theory, the radius of a graph is the minimum over all vertices u of the maximum distance from u to any other vertex of the graph.

### Distance (graph theory)

**diameterdistanceradius**

In graph theory, the radius of a graph is the minimum over all vertices u of the maximum distance from u to any other vertex of the graph.

### Collinearity

**collinearcollinear pointscolinear**

The radius of the circle that passes through the three non-collinear points

### Law of sines

**sine lawHyperbolic law of sinessine rule**

. This formula uses the law of sines.