# Streptohedron and Trapezohedron

Streptohedron and Trapezohedron

Take an -sided regular pyramid and form the union with its mirror image with respect to its base plane to get an -gonal bipyramid. Its faces are mutually congruent isosceles triangles. (With properly chosen height and =4 you get the regular octahedron as a special case.)

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Rotating its upper and lower parts by degrees yields a type of polyhedron called a streptohedron. Its faces are mutually congruent kites. It is also called a deltohedron or a trapezohedron.

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In contrast to trapezohedra, which exhibit only rotational symmetry, both streptohedra and bipyramids also have planes of symmetry that pass through their -fold axes (here only the axes of rotation are shown to avoid crowding).

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