正多面体

       空间中有几个平面多边形所围成的立体叫多面体。多面体有几面就叫几面体。有几个相同的正多边形围成的立体，在每一个顶点都集聚着同样数量的棱，而相邻的面都在相等的角下毗连，则称为“正多面体”。正多面体有且只有五种，即四、六、八、十二、二十面体。古希腊哲学家柏拉图早就已经知道这一点。因此，正多面体又称为柏拉图体。    

REGULAR POLYHEDRON

       The solid bounded by plane polygons in space is called a polyhedron. Different polyhedrons are formed by different number of polygons. If a polyhedron is formed by a number of identical regular polygons, the same number of edges will converge at each vertex, and contiguous polygons will neighbor each other at he same angle. This kind of polyhedron is also called a regular polyhedron. There are five and only five types of regular polyhedrons, i.e., tetrahedrons, hexahedrons, octahedrons, dodecahedrons and icosahedrons. The ancient Greek philosopher Plato knew this in his era, so this is also called Plato-polyhedron.plato knew this in his era so this is also called plato-polyhedron.