Feuerbach's Theorem
- 1. The Circle which passes through the feet of the Perpendiculars dropped from theVertices of any Triangle on the sides opposite them passes also through theMidpoints of these sides as well as through the Midpoint of the segments which join theVertices to the point of intersection of the Perpendicular (a Nine-PointCircle).
- 2. The Nine-Point Circle of any Triangle is Tangent internally to the Incircle andTangent externally to the three Excircles.
References
Coxeter, H. S. M. and Greitzer, S. L. Geometry Revisited. Washington, DC: Math. Assoc. Amer., pp. 117-119, 1967. Dixon, R. Mathographics. New York: Dover, p. 59, 1991.
- Truncated Icosahedron
- Truncated Icosidodecahedron
- Truncated Octahedral Number
- Truncated Octahedron
- Truncated Polyhedron
- Truncated Pyramid
- Truncated Square Pyramid
- Truncated Tetrahedral Number
- Truncated Tetrahedron
- Truncation
- Truth Table
- Tschebyshev
- Tschirnhausen Cubic
- Tschirnhausen Cubic Caustic
- Tschirnhausen Cubic Pedal Curve
- Tschirnhausen Transformation
- Tubular Neighborhood
- Tucker Circles
- Tukey's Biweight
- Tukey's Trimean
- Tunnel Number
- Turbine
- Turing Machine
- Turning Angle
- Turán Graph