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In geometry, a birotunda is any member of a family of dihedral-symmetric polyhedra, formed from two rotunda adjoined through the largest face. They are similar to a bicupola but instead of alternating squares and triangles, it alternates pentagons and triangles around an axis. There are two forms, ortho- and gyro-: an ''orthobirotunda'' has one of the two rotundas is placed as the mirror reflection of the other, while in a ''gyrobirotunda'' one rotunda is twisted relative to the other. The pentagonal birotundas can be formed with regular faces, one a Johnson solid, the other a semiregular polyhedron: * pentagonal orthobirotunda, * pentagonal gyrobirotunda, which is also called an icosidodecahedron. Other forms can be generated with dihedral symmetry and distorted equilateral pentagons. ==See also== *Gyroelongated pentagonal birotunda *Elongated pentagonal orthobirotunda *Elongated pentagonal gyrobirotunda 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Birotunda」の詳細全文を読む スポンサード リンク
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