# Decagon

## Decagon

Polygon with ten sides.

### Properties

A decagon has ten interior angles and 35 diagonals.

If the decagon is a regular decagon, then each of its interior angles measures 144°.

The apothem a of a regular decagon with a side length of c units is $$a = dfrac{c}{2 tan (frac{π}{10})}$$

### Formula

The formula to calculate the area A of a regular decagon of side length c is:
$$A=frac{5}{2}a^{2}sqrt{5+2sqrt{5}}$$

General decagon

Regular decagon