Bifrustum
In geometry, an -gonal bifrustum is a polyhedron composed of three parallel planes of -gons, with the middle plane largest and usually the top and bottom congruent.
It can be constructed as two congruent frusta combined across a plane of symmetry, and also as a bipyramid with the two polar vertices truncated.
They are duals to the family of elongated bipyramids.
Formulae
For a regular -gonal bifrustum with the equatorial polygon sides, bases sides and semi-height, the lateral surface area, total area and volume are:The volume V is twice the volume of a frustum.
Forms
Three bifrusta are duals to three Johnson solids,. In general, an -gonal bifrustum has trapezoids, 2 -gons, and is dual to the elongated dipyramids.| Triangular bifrustum | Square bifrustum | Pentagonal bifrustum |
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| 6 trapezoids, 2 triangles. Dual to elongated triangular bipyramid, | 8 trapezoids, 2 squares. Dual to elongated square bipyramid, | 10 trapezoids, 2 pentagons. Dual to elongated pentagonal bipyramid, |
