A pentagonal antiprism.
A prism is a polyhedron comprising two parallel polygons (bases) joined together by a set of quadrilaterals. In an antiprism, the two bases are twisted in respect of one another, and they are joined together by a series of triangles pointing in alternating direction.
There is no special name. In a prism it would be a quadrilateral, in an antiprism, a triangle.
It depends on the shape. The top of a pyramid will be a point (the apex). The top (and bottom) of a prism or an antiprism will be congruent polygons.
It could be a prism, but need not be. A regular dodecahedron, for example, is not a prism but has parallel and congruent pentagonal bases. You can also have any antiprism (see link).
A pentagonal antiprism.
A prism is a polyhedron comprising two parallel polygons (bases) joined together by a set of quadrilaterals. In an antiprism, the two bases are twisted in respect of one another, and they are joined together by a series of triangles pointing in alternating direction.
There is no special name. In a prism it would be a quadrilateral, in an antiprism, a triangle.
pentagonal antiprism, pentagonal deltohedron(not deltahedron), decagonal pyramid, and many more.
An octahedron is a closed 3-d shape with 8 polygonal faces. There are 257 topologically different convex octahedra. All but one are not antiprisms: only the regular octahedron is.An antiprism is a solid shape comprising two identical parallel faces joined together with a "ring" of triangles alternately pointing in opposite directions. Consider a regular octahedron placed on one of its faces - a triangle. Its top face will be another identical triangle which points in the opposite direction. Between the top and bottom, there are six triangles, alternately pointing up and down. It therefore meets all the requirements of an antiprism.
There are infinitely many possible answers. Common ones are are octagonal-based pyramid, an octagonal prism, on octagonal antiprism.
It depends on the shape. The top of a pyramid will be a point (the apex). The top (and bottom) of a prism or an antiprism will be congruent polygons.
In 2-dimensions, an octagon. In 3-d it could be a heptagonal pyramid, a quadrilateral prism or quadrilateral antiprism. There are probably a few more shapes.
A 26-sided shape is called a rhombicuboctahedron. It is known by other names such as snub square antiprism, elongated square gyrobicupola, and 26-agon.
A 26-sided shape is called a rhombicuboctahedron. It is known by other names such as snub square antiprism, elongated square gyrobicupola, and 26-agon.
If it has only two triangles then it is a triangle based prism. If it is has two n-sided polygonal faces and n triangles then it is a n-polygonal antiprism.
It could be a prism, but need not be. A regular dodecahedron, for example, is not a prism but has parallel and congruent pentagonal bases. You can also have any antiprism (see link).