Rotunda (geometry)

{{Short description|Solid made by joining an n- and 2n-gon with triangles and pentagons}}

{{Infobox polyhedron

| name = Set of rotundas

| image = Pentagonal rotunda.png

| caption = (Example: pentagonal rotunda)

| type =

| euler =

| faces = 1 {{mvar|n}}-gon
1 {{math|2n}}-gon
{{mvar|n}} pentagons
{{math|2n}} triangles

| edges = {{math|7n}}

| vertices = {{math|4n}}

| vertex_config =

| schläfli =

| wythoff =

| conway =

| coxeter =

| symmetry = {{math|Dihedral symmetry in three dimensions, [n], (*nn),}} order {{math|2n}}

| rotation_group = {{math|C{{sub|n}}, [n]{{sup|+}}, (nn),}} order {{mvar|n}}

| surface_area =

| volume =

| angle =

| dual =

| properties = convex

| vertex_figure =

| net =

| net_caption =

}}

In geometry, a rotunda is any member of a family of dihedral-symmetric polyhedra. They are similar to a cupola but instead of alternating squares and triangles, it alternates pentagons and triangles around an axis. The pentagonal rotunda is a Johnson solid.

Other forms can be generated with dihedral symmetry and distorted equilateral pentagons. {{examples|date=August 2020}}