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Sphere, surface produced by the rotation of a circle through 180° about one of its diameters. The intersection of a sphere and any plane is circular; should the plane pass through the center, the intersection is a great circle. The surface area of a sphere is 4 πr2, where r is the radius; its volume 4/3πr3. If mutually perpendicular x-, y-, and z- axes are constructed such that they intersect at the center, the sphere's equation is x2 + y2 + z2 =r2.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Sour gum to Stereotyping