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  2. Tetrahedron - Wikipedia

    en.wikipedia.org/wiki/Tetrahedron

    The dual of this solid is the triakis tetrahedron, a regular tetrahedron with four triangular pyramids attached to each of its faces. i.e., its kleetope. Regular tetrahedra alone do not tessellate (fill space), but if alternated with regular octahedra in the ratio of two tetrahedra to one octahedron, they form the alternated cubic honeycomb ...

  3. Pyramid (geometry) - Wikipedia

    en.wikipedia.org/wiki/Pyramid_(geometry)

    Each base edge and apex form a triangle, called a lateral face. A pyramid is a conic solid with a polygonal base. Many types of pyramids can be found by determining the shape of bases, either by based on a regular polygon (regular pyramids) or by cutting off the apex (truncated pyramid).

  4. Pyramid - Wikipedia

    en.wikipedia.org/wiki/Pyramid

    Pyramid of Khafre, Egypt, built c. 2600 BC. A pyramid (from Ancient Greek πυραμίς (puramís) 'pyramid') [1] [2] is a structure whose visible surfaces are triangular in broad outline and converge toward the top, making the appearance roughly a pyramid in the geometric sense.

  5. Tetrahedral number - Wikipedia

    en.wikipedia.org/wiki/Tetrahedral_number

    A pyramid with side length 5 contains 35 spheres. Each layer represents one of the first five triangular numbers. A tetrahedral number, or triangular pyramidal number, is a figurate number that represents a pyramid with a triangular base and three sides, called a tetrahedron.

  6. Polyhedron - Wikipedia

    en.wikipedia.org/wiki/Polyhedron

    Regular polyhedra are the most highly symmetrical. Altogether there are nine regular polyhedra: five convex and four star polyhedra. The five convex examples have been known since antiquity and are called the Platonic solids. These are the triangular pyramid or tetrahedron, cube, octahedron, dodecahedron and icosahedron:

  7. Hyperpyramid - Wikipedia

    en.wikipedia.org/wiki/Hyperpyramid

    In geometry, a hyperpyramid is a generalisation of the normal pyramid to n dimensions. In the case of the pyramid one connects all vertices of the base (a polygon in a plane) to a point outside the plane, which is the peak. The pyramid's height is the distance of the peak from the plane. This construction gets generalised to n dimensions.

  8. 5-cell - Wikipedia

    en.wikipedia.org/wiki/5-cell

    The tetrahedral pyramid is a special case of a 5-cell, a polyhedral pyramid, constructed as a regular tetrahedron base in a 3-space hyperplane, and an apex point above the hyperplane. The four sides of the pyramid are made of triangular pyramid cells. Many uniform 5-polytopes have tetrahedral pyramid vertex figures with Schläfli symbols ( )∨ ...

  9. Truncated triangular pyramid number - Wikipedia

    en.wikipedia.org/wiki/Truncated_Triangular...

    A pyramid with side length 5 contains 35 spheres. Each layer represents one of the first five triangular numbers. A truncated triangular pyramid number [1] is found by removing some smaller tetrahedral number (or triangular pyramidal number) from each of the vertices of a bigger tetrahedral number.