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 between them. Angles are usually measured in degrees (denoted), radians (denoted rad, or without a unit), or sometimes gradians (denoted grad). 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).
- ↑ Weisstein, Eric W. Angle. From MathWorld--A Wolfram Web Resource. Accessed 13 May 2010
- Degrees as an angle measure, with interactive animation (requires Java 2 Runtime Environment)
- Degree at MathWorld