. what is a polyhedron
A polyhedron is a 3-dimensional solid made from polygons. It has flat faces, straight edges, and vertices. For example, a cube, prism, or pyramid are polyhedrons. Cones, spheres, and cylinders are non-polyhedrons because their sides are not polygons and they have curved surfaces. The plural of a polyhedron is similarly called polyhedra. They are classified as prisms, pyramids, and platonic solids. For example, triangular prism, square prism, rectangular pyramid, square pyramid, and cube (platonic solid) are polyhedrons. Observe the following figure which indicates the different types of polyhedrons.