raadius

Raadius is the distance from the center of a circle or sphere to any point on its boundary. In two dimensions, this distance defines the circle’s radius; in three dimensions it defines the sphere’s radius. The symbol r is standard, though other variables may appear in different contexts.

For a circle of radius r, the circumference equals 2πr and the area equals πr^2. In a sphere with the same radius, the surface area is 4πr^2 and the volume is 4/3 πr^3. The diameter of a circle or sphere is twice the radius (d = 2r). All radii of a given circle or sphere are equal.

In higher dimensions, the concept extends to n-dimensional balls, where the radius is still the distance from the center to the boundary. In coordinate geometry, the radius can be described as the Euclidean distance from a center point to a boundary point. In polar or spherical coordinate systems, r often denotes the radial distance from the origin or a chosen center.

Linguistically, raadius is the Estonian term for radius and is used in similar mathematical contexts as the English term radius. The concept also appears in many scientific disciplines, including physics and engineering, where radii help characterize sizes, orbits, lenses, and other circular or spherical objects.

See also: Circle, Sphere, Diameter, Circumference, Surface area, Volume, Radius vector.