A dipyramid, also called a bipyramid, consists of two pyramids symmetrically placed base-to-base. The dipyramids are duals of the regular prisms. Their skeletons are the dipyramidal graphs.
The volume of a dipyramid of half-height and base area is equal to twice the volume of the corresponding pyramid, namely
(1)
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The volume of a dipyramid whose base is a regular -sided polygon with side is therefore
(2)
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The canonical dipyramids are the duals of the right regular equilateral prisms and if the original prism has edge length , the midradius of the dual dipyramid is
(3)
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An octagonal dipyramid is the convex hull of the second octahedron 2-compound.
The angles of the isocelese triangular faces in a canonical -dipyramid as illustrated above are given by
(4)
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(5)
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Nets for the canonical -dipyramids are illustrated above for to 10.
Johnson solid is a triangular dipyramid, the octahedron is a square dipyramid, and Johnson solid is a pentagonal dipyramid.