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  2. n-sphere - Wikipedia

    en.wikipedia.org/wiki/N-sphere

    The above ⁠ ⁠-sphere exists in ⁠ (+) ⁠-dimensional Euclidean space and is an example of an ⁠ ⁠-manifold. The volume form ⁠ ω {\displaystyle \omega } ⁠ of an ⁠ n {\displaystyle n} ⁠ -sphere of radius ⁠ r {\displaystyle r} ⁠ is given by

  3. Volume of an n-ball - Wikipedia

    en.wikipedia.org/wiki/Volume_of_an_n-ball

    where S n − 1 (r) is an (n − 1)-sphere of radius r (being the surface of an n-ball of radius r) and dA is the area element (equivalently, the (n − 1)-dimensional volume element). The surface area of the sphere satisfies a proportionality equation similar to the one for the volume of a ball: If A n − 1 ( r ) is the surface area of an ( n ...

  4. Eilenberg–Mazur swindle - Wikipedia

    en.wikipedia.org/wiki/Eilenberg–Mazur_swindle

    Example: The oriented n-manifolds have an addition operation given by connected sum, with 0 the n-sphere. If A + B is the n-sphere, then A + B + A + B + ... is Euclidean space so the Mazur swindle shows that the connected sum of A and Euclidean space is Euclidean space, which shows that A is the 1-point compactification of Euclidean space and ...

  5. Euclidean space - Wikipedia

    en.wikipedia.org/wiki/Euclidean_space

    Euclidean space is the fundamental space of geometry, intended to represent physical space. Originally, in Euclid's Elements, it was the three-dimensional space of Euclidean geometry, but in modern mathematics there are Euclidean spaces of any positive integer dimension n, which are called Euclidean n-spaces when one wants to specify their ...

  6. Manifold - Wikipedia

    en.wikipedia.org/wiki/Manifold

    The sphere is an example of a surface. The unit sphere of implicit equation. x 2 + y 2 + z 2 – 1 = 0. may be covered by an atlas of six charts: the plane z = 0 divides the sphere into two half spheres (z > 0 and z < 0), which may both be mapped on the disc x 2 + y 2 < 1 by the projection on the xy plane of coordinates. This provides two ...

  7. Euclidean geometry - Wikipedia

    en.wikipedia.org/wiki/Euclidean_geometry

    Euclid proved these results in various special cases such as the area of a circle [17] and the volume of a parallelepipedal solid. [18] Euclid determined some, but not all, of the relevant constants of proportionality. For instance, it was his successor Archimedes who proved that a sphere has 2/3 the volume of the circumscribing cylinder. [19]

  8. 3-sphere - Wikipedia

    en.wikipedia.org/wiki/3-sphere

    Direct projection of 3-sphere into 3D space and covered with surface grid, showing structure as stack of 3D spheres (2-spheres) In mathematics, a hypersphere or 3-sphere is a 4-dimensional analogue of a sphere, and is the 3-dimensional n-sphere. In 4-dimensional Euclidean space, it is the

  9. Horosphere - Wikipedia

    en.wikipedia.org/wiki/Horosphere

    The concept has its roots in a notion expressed by F. L. Wachter in 1816 in a letter to his teacher Gauss.Noting that in Euclidean geometry the limit of a sphere as its radius tends to infinity is a plane, Wachter affirmed that even if the fifth postulate were false, there would nevertheless be a geometry on the surface identical with that of the ordinary plane. [1]