Quadrilaterals

• Aubel's Theorem
• Bicentric Quadrilateral
• Bimedian
• Brahmagupta's Formula
• Brahmagupta's Theorem
• Brahmagupta's Trapezium
• Bretschneider's Formula
• Complete Quadrangle
• Complete Quadrilateral
• Cyclic Quadrangle
• Cyclic Quadrilateral
• Diagonal Points
• Diagonal Triangle
• Diamond
• Equilic Quadrilateral
• Fano's Axiom
• Fuss's Problem
• Gauss-Bodenmiller Theorem
• Golden Rhombus
• Hesse's Theorem
• Isosceles Trapezium
• Isosceles Trapezoid
• Kite
• Léon Anne's Theorem
• Lozenge
• Medial Parallelogram
• Nine-Point Conic
• Orthocentric Centroid
• Orthocentric Quadrangle
• Orthocentric Quadrilateral
• Orthopolar Line
• Parallelogram
• Poncelet's Coaxal Theorem
• Ptolemy Inequality
• Ptolemy's Theorem
• Quadrangle
• Quadrilateral
• Quadrilateral Tiling
• Rational Quadrilateral
• Rectangle
• Rhomb
• Rhomboid
• Rhombus
• Right Trapezoid
• Skew Quadrilateral
• Square
• Strombus
• Sylvester's Four-Point Problem
• Tangential Quadrilateral
• Trapezium
• Trapezoid
• van Aubel's Theorem
• Varignon Parallelogram
• Varignon's Theorem
• Watt's Parallelogram
• Wittenbauer's Parallelogram
• Wittenbauer's Theorem