# 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
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.

### Centre (geometry)

centercentrecenters
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.

### 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.