Ptolemy's Theorem
If a Quadrilateral is inscribed in a circle (i.e., for a cyclic quadrilateral), the sum of the products of the two pairsof opposite sides equals the product of the diagonals
This fact can be used to derive the Trigonometry addition formulas.See also Fuhrmann's Theorem, Ptolemy Inequality
References
Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 42-43, 1967.
- Positive
- Positive Definite Function
- Positive Definite Matrix
- Positive Definite Quadratic Form
- Positive Definite Tensor
- Positive Integer
- Positive Semidefinite Matrix
- Positive Semidefinite Quadratic Form
- Postage Stamp Problem
- Posterior Distribution
- Postnikov System
- Postulate
- Potato Paradox
- Potential Function
- Potential Theory
- Pothenot Problem
- Poulet Number
- Power
- Power Center
- Power (Circle)
- Power Curve
- Powerfree
- Powerful Number
- Power Line
- Power Point