Directed Angle
The symbol 
denotes the directed angle from 
to 
, which is the signed angle through which mustbe rotated about 
to coincide with . Four points 
lie on a Circle (i.e., are Concyclic) Iff 
. Itis also true that
Three points
, , and 
are Collinear Iff 
or 
. For any four points, , , , and
,
See also Angle, Collinear, Concyclic, Miquel Equation
References
Johnson, R. A. Modern Geometry: An Elementary Treatise on the Geometry of the Triangle and the Circle. Boston, MA: Houghton Mifflin, pp. 11-15, 1929.
- Sporadic Group
- Sports
- Sprague-Grundy Function
- Sprague-Grundy Number
- Sprague-Grundy Value
- Spread (Link)
- Spread (Tree)
- Spun Knot
- Squarable
- Square
- Square Bracket Polynomial
- Square Cupola
- Square Curve
- Square Cutting
- Squared
- Squared Square
- Square-Free
- Squarefree
- Butterfly Catastrophe
- Butterfly Curve
- Butterfly Effect
- Butterfly Fractal
- Butterfly Polyiamond
- Butterfly Theorem
- Bäcklund Transformation