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:

\( A=frac{5}{2}a^{2}sqrt{5+2sqrt{5}} \)

### Examples

General decagon

Regular decagon