Decagon
The constructible regular 10-sided Polygon with Schläfli Symbol 
. TheInradius 
, Circumradius 
, and Area can be computed directly from the formulas for a generalregular Polygon with side length 
and 
sides,
 |  |  | (1) |
 | |  | (2) |
 | |  | (3) |
Here,
is the Golden Mean.See also Decagram, Dodecagon, Trigonometry Values Pi/10, Undecagon
References
Dixon, R. Mathographics. New York: Dover, p. 18, 1991.
- d'Alembert Ratio Test
- d'Alembert's Equation
- d'Alembert's Solution
- d'Alembert's Theorem
- Damped Exponential Cosine Integral
- d-Analog
- Dandelin Spheres
- Danielson-Lanczos Lemma
- Darboux Integral
- Darboux-Stieltjes Integral
- Darboux Vector
- Darling's Products
- Dart
- Darwin-de Sitter Spheroid
- Darwin's Expansions
- Database
- Data Structure
- Daubechies Wavelet Filter
- Davenport-Schinzel Sequence
- Dawson's Integral
- Day of Week
- de Bruijn Constant
- de Bruijn Diagram
- de Bruijn Graph
- de Bruijn-Newman Constant