A heptagon has 14 diagonals. 

You mightn't have known:

-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.

- 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: \(\dfrac{n\left(n-3\right)}{2}\), where n is the number of vertices of the polygon.

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(SORRY I'M BEING A LITTE BIT SHOWING OFF)