Triangle Properties
- 3, 4, 5 Triangle
- AAA Theorem
- AAS Theorem
- Actual Trilinear Coordinates
- Adjacent Side
- Alhazen's Billiard Problem
- Anticomplement
- Anticomplementary Conjugate
- Apex
- Area Principle
- Areal Coordinates
- ASA Theorem
- ASS Theorem
- Barycentric Coordinates
- Bicentric Triangle
- Bride's Chair
- Brocard Angle
- Brocard Geometry
- Carnot's Theorem
- Cathetus
- Cevapoint
- Cevian Transform
- Chasles's Polars Theorem
- Cleaver
- Conway Triangle Notation
- Cross Conjugate
- Crossed Ladders Theorem
- de Finetti Diagram
- Desargues' Theorem
- Donkin's Theorem
- Droz-Farny Line Theorem
- Droz-Farny Theorem
- Equilateral Triangle Line Picking
- Erdős-Mordell Theorem
- Euler Triangle Formula
- Euler's Triangle Theorem
- Exact Trilinear Coordinates
- Exterior Angle Theorem
- Fagnano's Inequality
- Fagnano's Problem
- Fermat's Problem
- Fermat's Right Triangle Theorem
- Feuerbach's Theorem
- Fontené Theorems
- Garfunkel's Inequality
- Griffiths' Theorem
- Heron's Formula
- Hinge Theorem
- Homogeneous Barycentric Coordinates
- Hypotenuse
- Inner Pentagon Point
- Isoconjugation
- Isogonal Transform
- Isosceles Right Triangle Line Picking
- Isotomic Transform
- Kosnita Theorem
- Leg
- Lemoine-Brocard Geometry
- Lemoine Geometry
- Lemoine's Problem
- Maltitude
- Medial Triangle Locus Theorem
- Morley's Theorem
- Musselman's Theorem
- Napoleon Crossdifference
- Napoleon's Theorem
- Newton's Formulas
- Ono Inequality
- Opposite Side
- Orthocentric System
- Orthocorrespondent
- Orthotransversal
- Outer Pentagon Point
- Parallelian
- Pasch's Axiom
- Peacock Tail
- Petr-Douglas-Neumann Theorem
- Petr-Neumann-Douglas Theorem
- Pompeiu's Theorem
- Pons Asinorum
- Power Curve
- Purser's Theorem
- Pythagorean Fraction
- Pythagorean Theorem
- Pythagorean Triad
- Pythagorean Triangle
- Pythagorean Triple
- Radiation Symbol Theorem
- RAT-Free Set
- Reciprocal Conjugation
- SAS Theorem
- Schoute's Theorem
- Seydewitz's Theorem
- Simplex Plot
- SSS Theorem
- Steiner Angles
- Steiner-Lehmus Theorem
- Ternary Diagram
- Ternary Graph
- Ternary Plot
- Thomsen's Figure
- Triangle Arcs
- Triangle Area
- Triangle Circumscribing
- Triangle Counting
- Triangle Geometry
- Triangle Interior
- Triangle Line Picking
- Triangle Median
- Triangle Packing
- Triangle Pentagon Erecting
- Triangle Plot
- Triangle Point Picking
- Triangle Postulate
- Triangle Power
- Triangle Space
- Triangle Square Inscribing
- Triangle Squaring
- Triangle Tiling
- Trilinear Coordinates
- Trilinear Quotient
- Trilinear Vertex Matrix
- Tripolar
- Tripolar Coordinates
- Tripole
- Tweedie's Theorem
- Twin Pythagorean Triple
- Viviani's Theorem
- Windmill