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  2. Hilbert's third problem - Wikipedia

    en.wikipedia.org/wiki/Hilbert's_third_problem

    Therefore, these two shapes cannot be scissors-congruent. A polyhedron's invariant is defined based on the lengths of its edges and the angles between its faces. If a polyhedron is cut into two, some edges are cut into two, and the corresponding contributions to the Dehn invariants should therefore be additive in the edge lengths.

  3. Dihedral angle - Wikipedia

    en.wikipedia.org/wiki/Dihedral_angle

    A dihedral angle is the angle between two intersecting planes or half-planes. It is a plane angle formed on a third plane, perpendicular to the line of intersection between the two planes or the common edge between the two half-planes. In higher dimensions, a dihedral angle represents the angle between two hyperplanes.

  4. Regular icosahedron - Wikipedia

    en.wikipedia.org/wiki/Regular_icosahedron

    The dihedral angle of a pentagonal antiprism between pentagon-to-triangle is 100.8°, and the dihedral angle of a pentagonal pyramid between the same faces is 37.4°. Therefore, for the regular icosahedron, the dihedral angle between two adjacent triangles, on the edge where the pentagonal pyramid and pentagonal antiprism are attached is 37.4 ...

  5. Elongated triangular cupola - Wikipedia

    en.wikipedia.org/wiki/Elongated_triangular_cupola

    the dihedral angle of an elongated triangular cupola between two adjacent squares is that of a hexagonal prism, the internal angle of its base 120°; the dihedral angle of a hexagonal prism between square-to-hexagon is 90°, that of a triangular cupola between square-to-hexagon is 54.7°, and that of a triangular cupola between triangle-to ...

  6. 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 ...

  7. Rhombicuboctahedron - Wikipedia

    en.wikipedia.org/wiki/Rhombicuboctahedron

    The dihedral angle between square-to-triangle, on the edge where a square cupola is attached to an octagonal prism is the sum of the dihedral angle of a square cupola triangle-to-octagon and the dihedral angle of an octagonal prism square-to-octagon 54.7° + 90° = 144.7°. Therefore, the dihedral angle of a rhombicuboctahedron for every square ...

  8. Prism (geometry) - Wikipedia

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

    Example truncated triangular prism. Its top face is truncated at an oblique angle, but it is not an oblique prism. A truncated prism is formed when prism is sliced by a plane that is not parallel to its bases. A truncated prism's bases are not congruent, and its sides are not parallelograms. [7]

  9. Elongated square gyrobicupola - Wikipedia

    en.wikipedia.org/wiki/Elongated_square_gyrobicupola

    The dihedral angle between square-to-triangle, on the edge where a square cupola is attached to an octagonal prism is the sum of the dihedral angle of a square cupola triangle-to-octagon and the dihedral angle of an octagonal prism square-to-octagon 54.7° + 90° = 144.7°. Therefore, the dihedral angle of a rhombicuboctahedron for every square ...