Angle -- from Wolfram MathWorld

Given two intersecting lines or line segments, the amount of rotation about the point of intersection (the vertex) required to bring one into correspondence with the other is called the angle theta between them. The term "plane angle" is sometimes used to distinguish angles in a plane from solid angles measured in space (International Standards Organization 1982, p. 5). The term "angle" can also be applied to the rotational offset between intersecting planes about their

Central Angle -- from Wolfram MathWorld

Distance between Two Fermat Points - Wolfram Demonstrations Project

Line -- from Wolfram MathWorld, line

Line-Line Angle -- from Wolfram MathWorld

Polar Angle -- from Wolfram MathWorld

Line -- from Wolfram MathWorld, line

anna – Page 2 – Picture this maths

Angles: Definition, Parts, Types, Degrees, Properties, Examples

Wolfram Mathworld in the Notebook Archive

Angles: Definition, Parts, Types, Degrees, Properties, Examples

Steiner Angles -- from Wolfram MathWorld

Wolfram, Alpha Meets MathWorld—Wolfram

Cubic Spline - From Wolfram MathWorld, PDF