Nonagon
The unconstructible regular Polygon with nine sides and Schläfli Symbol 
. It issometimes called an Enneagon.
Although the regular nonagon is not a Constructible Polygon, Dixon (1991) gives several close approximations. Whilethe Angle subtended by a side is 
, Dixon gives constructions containing angles of
and 
.
Madachy (1979) illustrates how to construct a nonagon by folding and knotting a strip of paper.
See also Nonagram, Trigonometry Values Pi/9
References
Dixon, R. Mathographics. New York: Dover, pp. 40-44, 1991. Madachy, J. S. Madachy's Mathematical Recreations. New York: Dover, pp. 60-61, 1979.
- Zonotype
- Zorn's Lemma
- z-Score
- Zsigmondy Theorem
- Z-Transform
- z-Transform
- z-Transform (Population)
- Embeddable Knot
- Embedding
- Empty Set
- e-Multiperfect Number
- Enantiomer
- Enantiomorph
- Encoding
- Endogenous Variable
- Endomorphism
- Endraß Octic
- Energy
- En-Function
- Engel's Theorem
- Enneacontagon
- Enneacontahedron
- Enneadecagon
- Enneagon
- Enneagonal Number