Sphere
From AoPSWiki
A sphere is the collection of points in space which are equidistant from a fixed point. This point is called the center of the sphere. The common distance of the points of the sphere from the center is called the radius.
Spheres are the natural 3-dimensional analog of circles.
The volume of a sphere is 
, where r is the radius of the sphere.
The surface area of a sphere is 
, where r is the radius.
See also
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