Polygon with eleven sides.

- A hendecagon is considered regular if all of its sides are the same length and if all of its interior angles have the same measure.
- If the hendecagon is regular, each of its interior angles measures about 147.3°.

### Formula

The formula to calculate the area

*A*of a regular hendecagon with side*c*is:*A*=\(\frac{11{c}^{2}}{4}\textrm{cot(π/11)}\).

### Examples

Here is a regular hendecagon where the measure of an interior angle is expressed as a mixed number:

The Canadian one dollar coin is in the shape of a **regular** hendecagon.

### Etymological Note

- This word comes from three Greek words:
*hens*(one more),*deca*(ten) and*gon*(angle). - Some authors use the term
**undecagon**which comes from a Latin prefix (*uno*) and two Greek words.

### Historical Note

The ramparts of Nicosia, the capital of Cyprus, were built by the Venitians following a circular plan where the eleven bastions occupy the vertices of a regular hendecagon.