Octagon
The regular 8-sided Polygon. The Inradius 
, Circumradius 
, and Area 
can be computeddirectly from the formulas for a general regular Polygon with side length 
and 
sides,
 |  |  | (1) |
 | |  | (2) |
 | |  | (3) |
See also Octahedron, Polygon, Regular Polygon, Trigonometry Values Pi/8
- Rhombicosahedron
- Rhombicosidodecahedron
- Rhombic Polyhedron
- Rhombic Triacontahedron
- Rhombicuboctahedron
- Rhombidodecadodecahedron
- Rhombihexacron
- Rhombihexahedron
- Rhombitruncated Cuboctahedron
- Rhombitruncated Icosidodecahedron
- Rhombohedron
- Rhomboid
- Rhomboidal Dodecahedron
- Rhombus
- Rhumb Line
- Ribbon Knot
- Ribet's Theorem
- Riccati-Bessel Functions
- Riccati Differential Equation
- Ricci Curvature
- Ricci Tensor
- Rice Distribution
- Richardson Extrapolation
- Richardson's Theorem
- Richard's Paradox