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In solid geometry, a face is a flat (planar) surface that forms part of the boundary of a solid object; a three-dimensional solid bounded exclusively by flat faces is a polyhedron. In more technical treatments of the geometry of polyhedra and higher-dimensional polytopes, the term is also used to mean an element of any dimension of a more general polytope (in any number of dimensions).〔.〕 ==Polygonal face== In elementary geometry, a face is a two-dimensional polygon on the boundary of a polyhedron.〔〔.〕 Other names for a polygonal face include side of a polyhedron, and tile of a Euclidean plane tessellation. For example, any of the six squares that bound a cube is a face of the cube. Sometimes "face" is also used to refer to the 2-dimensional features of a 4-polytope. With this meaning, the 4-dimensional tesseract has 24 square faces, each sharing two of 8 cubic cells. ! ! ! |- align=center valign=top | The cube has 3 square ''faces'' per vertex. |100px The small stellated dodecahedron has 5 pentagrammic faces per vertex. | The square tiling in the Euclidean plane has 4 square ''faces'' per vertex. |100px The order-5 square tiling has 5 square ''faces'' per vertex. |100px The tesseract has 3 square ''faces'' per edge. |} Some other polygons, which are not faces, are also important for polyhedra and tessellations. These include Petrie polygons, vertex figures and facets (flat polygons formed by coplanar vertices which do not lie in the same face of the polyhedron). 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「Face (geometry)」の詳細全文を読む スポンサード リンク
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