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  2. Tetrahedron - Wikipedia

    en.wikipedia.org/wiki/Tetrahedron

    A regular tetrahedron is a tetrahedron in which all ... of the 1st century Heron's formula for the area of a ... by an irregular triangulated surface, and irregular ...

  3. Surface area - Wikipedia

    en.wikipedia.org/wiki/Surface_area

    A sphere of radius r has surface area 4πr 2.. The surface area (symbol A) of a solid object is a measure of the total area that the surface of the object occupies. [1] The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc length of one-dimensional curves, or of the surface area for polyhedra (i.e., objects with ...

  4. List of formulas in elementary geometry - Wikipedia

    en.wikipedia.org/wiki/List_of_formulas_in...

    The basic quantities describing a sphere (meaning a 2-sphere, a 2-dimensional surface inside 3-dimensional space) will be denoted by the following variables r {\displaystyle r} is the radius, C = 2 π r {\displaystyle C=2\pi r} is the circumference (the length of any one of its great circles ),

  5. Platonic solid - Wikipedia

    en.wikipedia.org/wiki/Platonic_solid

    This follows from the spherical excess formula for a spherical polygon and the fact that the vertex figure of the polyhedron {p,q} is a regular q-gon. The solid angle of a face subtended from the center of a platonic solid is equal to the solid angle of a full sphere (4 π steradians) divided by the number of faces.

  6. Truncated tetrahedron - Wikipedia

    en.wikipedia.org/wiki/Truncated_tetrahedron

    Given the edge length .The surface area of a truncated tetrahedron is the sum of 4 regular hexagons and 4 equilateral triangles' area, and its volume is: [2] =, =.. The dihedral angle of a truncated tetrahedron between triangle-to-hexagon is approximately 109.47°, and that between adjacent hexagonal faces is approximately 70.53°.

  7. Regular polyhedron - Wikipedia

    en.wikipedia.org/wiki/Regular_polyhedron

    The tetrahedron, cube, and octahedron ... Abstract regular polytopes remain an active area of research. ... On a spherical surface, the regular polyhedron {2, ...

  8. Polyhedron - Wikipedia

    en.wikipedia.org/wiki/Polyhedron

    The surface area of a polyhedron is the sum of ... Simple families of solids may have simple formulas for their ... the rotation group for a regular tetrahedron; ...

  9. De quinque corporibus regularibus - Wikipedia

    en.wikipedia.org/wiki/De_quinque_corporibus...

    Truncated icosahedron, one of the Archimedean solids illustrated in De quinque corporibus regularibus. The five Platonic solids (the regular tetrahedron, cube, octahedron, dodecahedron, and icosahedron) were known to della Francesca through two classical sources: Timaeus, in which Plato theorizes that four of them correspond to the classical elements making up the world (with the fifth, the ...