| Family of bifrusta | |||||||||
| Faces: | -gons trapezoids | ||||||||
| Surface Area: | \begin{align} &n(a+b)\sqrt{\left(\tfrac{a-b}{2}\cot{\tfrac{\pi}{n}}\right)2+h2}\\[2pt] & + n
| ||||||||
| Volume: | n
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| Dual: | Elongated bipyramids | ||||||||
| Properties: | convex | ||||||||
In geometry, an -agonal bifrustum is a polyhedron composed of three parallel planes of -agons, 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.[1]
They are duals to the family of elongated bipyramids.
For a regular -gonal bifrustum with the equatorial polygon sides, bases sides and semi-height (half the distance between the planes of bases), the lateral surface area, total area and volume are:[2] and [3] Note that the volume V is twice the volume of a frusta.
Three bifrusta are duals to three Johnson solids, . In general, a -agonal bifrustum has trapezoids, 2 -agons, and is dual to the elongated dipyramids.