Rodrigues's Curvature Formula
where
is the unit Normal Vector and 
is one of the two Principal Curvatures.See also Normal Vector, Principal Curvatures- Reptend Prime
- Rep-Tile
- Repunit
- Residual
- Residual vs. Predictor Plot
- Residue Class
- Residue (Complex Analysis)
- Residue (Congruence)
- Residue Index
- Residue Theorem (Complex Analysis)
- Residue Theorem (Group)
- Resolution
- Resolution Class
- Resolution Modulus
- Resolvable
- Resolving Tree
- Resonance Overlap
- Resonance Overlap Method
- R-Estimate
- Restricted Divisor Function
- Restricted Growth Function
- Restricted Growth String
- Resultant
- Retardance
- Reuleaux Polygon