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°.


The formula to calculate the area A of a regular hendecagon with side c is:
A =\(\frac{11{c}^{2}}{4}\textrm{cot(π/11)}\).


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.

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