Parseval's Integral
The Poisson Integral with 
.
where
is a Bessel Function of the First Kind and 
is a Gamma Function.- Rotoinversion
- Rotor
- Rotunda
- Rouché's Theorem
- Roulette
- Round
- Rounding
- Routh-Hurwitz Theorem
- Routh's Theorem
- RSA Encryption
- RSA Number
- Rubber-Sheet Geometry
- Rubik's Clock
- Rubik's Cube
- Rudin-Shapiro Sequence
- Rudvalis Group
- Rule
- Ruled Surface
- Rule of 72
- Ruler
- Ruler Function
- Ruling
- Run
- Runge-Kutta Method
- Runge-Walsh Theorem