Perpendicular Bisector
The perpendicular bisectors of a Triangle 
are lines passing through the Midpoint 
of eachside which are Perpendicular to the given side. A Triangle's three perpendicular bisectors meet ata point 
known as the Circumcenter (which is also the center of the Triangle's Circumcircle).
- 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
- Ridders' Method
- Ridge
- Riemann-Christoffel Tensor
- Riemann Curve Theorem
- Riemann Differential Equation
- Riemann Function