A heptagon has 14 diagonals. In geometry, a diagonal refers to a side joining nonadjacent vertices in a closed plane figure known as a polygon. The formula for calculating the number of diagonals for any polygon is given as: n (n - 3) / 2, where n is the number of vertices of the polygon.
A heptagon is a type of polygon, which is a closed plane figure bounded by seven straight edges containing seven angles. When all the sides and angles are equilateral and equiangular, respectively, the heptagon is said to be a regular heptagon. Other types of polygons are triangles, quadrilaterals, pentagons, hexagons and octagons.