Bifrustum

{{short description|Polyhedron made by joining two identical frusta at their bases}}

{{Infobox polyhedron

| name = Family of bifrusta

| image = Hexagonal bifrustum.png

| caption = Example: hexagonal bifrustum

| type =

| euler =

| faces = {{math|2}} polygons
{{math|2n}} trapezoids

| edges = {{math|5n}}

| vertices = {{math|3n}}

| vertex_config =

| schläfli =

| wythoff =

| conway =

| coxeter =

| symmetry = {{math|D_nh, [n,2], (*n22)}}

| rotation_group =

| surface_area = $\backslash begin\{align\}$

&n (a+b) \sqrt{\left(\tfrac{a-b}{2} \cot{\tfrac{\pi}{n}}\right)^2+h^2} \\[2pt]

& \ \ +\ n \frac{b^2}{2 \tan{\frac{\pi}{n}}}

\end{align}

| volume = $n\; \backslash frac\{a^2+b^2+ab\}\{6\; \backslash tan\{\backslash frac\{\backslash pi\}\{n\}\}\}h$

| angle =

| dual = Elongated bipyramids

| properties = convex

| vertex_figure =

| net =

| net_caption =

}}

In geometry, an {{mvar|n}}-agonal bifrustum is a polyhedron composed of three parallel planes of polygon, 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.{{Cite web |title=Octagonal Bifrustum |url=https://etc.usf.edu/clipart/42700/42718/bifrustum-02_42718.htm |access-date=2022-06-16 |website=etc.usf.edu |language=en}}

They are duals to the family of elongated bipyramids.