Inflection Point
A point on a curve at which the Sign of the Curvature (i.e., the concavity) changes. The First DerivativeTest can sometimes distinguish inflection points from Extrema for Differentiable functions 
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- Soddy Circles
- Soddy Line
- Soddy Points
- Soddy's Hexlet
- Sofa Constant
- Soldner's Constant
- Solenoidal Field
- Sol Geometry
- Solid
- Solid Angle
- Solid Geometry
- Solid of Revolution
- Solid Partition
- Solidus
- Solitary Number
- Soliton
- Solomon's Seal Knot
- Solomon's Seal Lines
- Solomon's Seal Polygon
- Solvable Congruence
- Solvable Group
- Solvable Lie Group
- Soma Cube
- Somer-Lucas Pseudoprime
- Sommerfeld's Formula