Principal Radius of Curvature
At each point on a given a 2-D Surface, there are two ``principal'' Radii of Curvature. The larger is denoted 
, and the smaller 
. The ``principal directions'' corresponding tothe principal radii of curvature are Perpendicular to one another. In other words, the surface normalplanes at the point and in the principal directions are Perpendicular to one another, and both arePerpendicular to the surface tangent plane at the point.
- Quartic Surface
- Quartile
- Quartile Deviation
- Quartile Range
- Quartile Skewness Coefficient
- Quartile Variation Coefficient
- Quasiamicable Pair
- Quasiconformal Map
- Quasigroup
- Quasiperfect Number
- Quasiperiodic Function
- Quasiperiodic Motion
- Quasirandom Sequence
- Quasiregular Polyhedron
- Quasirhombicosidodecahedron
- Quasirhombicuboctahedron
- Quasisimple Group
- Quasithin Theorem
- Quasitruncated Cuboctahedron
- Quasitruncated Dodecadocahedron
- Quasitruncated Dodecahedron
- Quasitruncated Great Stellated Dodecahedron
- Quasitruncated Hexahedron
- Quasitruncated Small Stellated Dodecahedron
- Quasi-Unipotent Group