Butterfly Theorem
Given a Chord 
of a Circle, draw any other two Chords 
and 
passing through its Midpoint. Call the points where 
and 
meet 
and 
. Then 
is the Midpoint of 
.
References
Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 45-46, 1967.
- Product Formula
- Product-Moment Coefficient of Correlation
- Product Neighborhood
- Product Rule
- Product Space
- Program
- Projection
- Projection Operator
- Projective Collineation
- Projective General Linear Group
- Projective General Orthogonal Group
- Projective General Unitary Group
- Projective Geometry
- Projective Plane
- Projective Plane PK2
- Projective Space
- Projective Special Linear Group
- Projective Special Orthogonal Group
- Projective Special Unitary Group
- Projective Symplectic Group
- Projectivity
- Prolate Cycloid
- Prolate Cycloid Evolute
- Prolate Spheroid
- Prolate Spheroidal Coordinates