Curvature Scalar
The curvature scalar is given by
where
is the Metric Tensor and 
is the Ricci Tensor.See also Curvature, Gaussian Curvature, Mean Curvature, Metric Tensor, Radius of Curvature,Ricci Tensor, Riemann-Christoffel Tensor- Archimedes' Postulate
- Archimedes' Problem
- Archimedes' Recurrence Formula
- Archimedes' Spiral
- Archimedes' Spiral Inverse
- Arc Length
- Arc Minute
- Arcsecant
- Arc Second
- Arcsine
- Arctangent
- Area
- Area Element
- Areal Coordinates
- Area-Preserving Map
- Area Principle
- Arf Invariant
- Argand Diagram
- Argand Plane
- Argoh's Conjecture
- Argument Addition Relation
- Argument (Complex Number)
- Argument (Elliptic Integral)
- Argument (Function)
- Argument Multiplication Relation