A five-sided shape is called a pentagon. In geometry, all two dimensional shapes are known as polygons, so it can also be referred to as a five-sided polygon. More »

A 15-sided shape may be called a pentadecagon or pentakaidecagon, depending on who is doing the naming. More often, it is a polygon, which is an enclosed shape with any number of sides that do not cross. Polygons can be ... More »

A seven-sided shape is called a heptagon. A heptagon is one type of polygon, which can have any number of sides. More »

A pentagon has five diagonals on the inside of the shape. The diagonals of any polygon can be calculated using the formula n*(n-3)/2, where "n" is the number of sides. In the case of a pentagon, which "n" will be 5, the ... More »

One term used for a 3D pentagon is a shape called a pentagonal prism. According to Reference.com, this is the polygon that results when you take a pentagon, transcribe a copy of it, and connect the two pentagons using fi... More »

Usually when a person refers to a "three-dimensional pentagon," he is referring to a regular dodecahedron. A dodecahedron is a solid made of 12 flat faces, and a regular dodecahedron is made of 12 regular pentagons. More »

To calculate the area of a regular pentagon, the perimeter of the polygon is multiplied by the apothem and the result is divided in half. The mathematical formula for the calculation is area = (apothem x perimeter)/2. More »