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  2. Tetrahedron - Wikipedia

    en.wikipedia.org/wiki/Tetrahedron

    A triangular pyramid has Schläfli symbol {3}∨( ). C 3v C 3 [3] ... Three angles are the angles of some triangle if and only if their sum is 180° (π radians ...

  3. Pyramid (geometry) - Wikipedia

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

    Rarely, a right pyramid is defined to be a pyramid whose base is circumscribed about a circle and the altitude of the pyramid meets the base at the circle's center. [ 17 ] For the pyramid with an n - sided regular base, it has n + 1 vertices, n + 1 faces, and 2 n edges. [ 18 ]

  4. Solid angle - Wikipedia

    en.wikipedia.org/wiki/Solid_angle

    The solid angle of a four-sided right rectangular pyramid with apex angles a and b (dihedral angles measured to the opposite side faces of the pyramid) is = ⁡ (⁡ ⁡ ()). If both the side lengths ( α and β ) of the base of the pyramid and the distance ( d ) from the center of the base rectangle to the apex of the pyramid (the center of ...

  5. Sierpiński triangle - Wikipedia

    en.wikipedia.org/wiki/Sierpiński_triangle

    Sierpiński pyramid recursion (8 steps) The Sierpiński tetrahedron or tetrix is the three-dimensional analogue of the Sierpiński triangle, formed by repeatedly shrinking a regular tetrahedron to one half its original height, putting together four copies of this tetrahedron with corners touching, and then repeating the process.

  6. Triangular bipyramid - Wikipedia

    en.wikipedia.org/wiki/Triangular_bipyramid

    A triangular bipyramid with regular faces is numbered as the twelfth Johnson solid . [10] It is an example of a composite polyhedron because it is constructed by attaching two regular tetrahedra. [11] [12] A triangular bipyramid's surface area is six times that of each triangle

  7. 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.

  8. Elongated triangular bipyramid - Wikipedia

    en.wikipedia.org/wiki/Elongated_triangular_bipyramid

    The dihedral angle of an elongated triangular bipyramid can be calculated by adding the angle of the tetrahedron and the triangular prism: [5] the dihedral angle of a tetrahedron between two adjacent triangular faces is arccos ⁡ ( 1 3 ) ≈ 70.5 ∘ {\textstyle \arccos \left({\frac {1}{3}}\right)\approx 70.5^{\circ }} ;

  9. Elongated triangular pyramid - Wikipedia

    en.wikipedia.org/wiki/Elongated_triangular_pyramid

    An elongated triangular pyramid with edge length has a height, by adding the height of a regular tetrahedron and a triangular prism: [4] (+). Its surface area can be calculated by adding the area of all eight equilateral triangles and three squares: [2] (+), and its volume can be calculated by slicing it into a regular tetrahedron and a prism, adding their volume up: [2]: ((+)).