Quadrilaterals, Theorems and Problems, page 4 of 4

Go Geometry: Quadrilaterals

The Incas used trapezoids for all their windows and doors, which withstand earthquakes well.

Quadrilaterals: Table of Content (Page 4 of 4)

 

Inca Skull Surgery

 

 

Square
Proposed Problem 76: Area of a Circle
. Square, Circle, Circular Sector. 

 

Proposed Problem 74: Three Intersecting Circles. Cyclic quadrilateral, Angles.

 

Proposed Problem 73: Three Intersecting Circles. Cyclic quadrilateral.

 

 

Proposed Problem 72: Intersecting Circles. Cyclic quadrilateral, Chords, Parallel.

 

 

Proposed Problem 71: Cyclic Quadrilateral.

 

 

Proposed Problem 70: Squares inscribed in a triangle, Similarity.

 

 

Proposed Problem 69: Square inscribed in a triangle, Similarity.

 

 

Proposed Problem 67: Triangle, Circumcircle, Angles, Cyclic Quadrilateral.
 

 

Four Circles Theorem Using TracenPoche Dynamic Software
Step-by-Step construction, Manipulation, and animation.

 

Proposed Problem 63: Heptagon Regular, Side and Diagonals.

 

Proposed Problem 62: Square Diagonal, Inscribed Circle.

 

 

Arbelos, Inscribed Circle and Concyclic Points Cyclic Quadrilateral.

 

Casey Theorem 

Casey's Theorem. Generalized Ptolemy's Theorem.

 

Proposed Problem 57 

Proposed Problem 57: Angle bisector, circles Cyclic Quadrilateral.

 

Proposed Problem 55 

Proposed Problem 55: Angle bisector, circles Cyclic Quadrilateral.

 

Generalizing Van Aubel: Michael de Villiers' Theorems.
 

 

Eyeball Theorem: Animated Angle to Geometry Study.

 

Eyeball to Eyeball Theorem

Presentation: "Animated Angle to Geometry Study I & II." 46th Annual Georgia Mathematics Conference, Extreme Makeover: Mathematics Edition!, Rock Eagle, October 20-22, 2005,

 

Hippocrates and Squaring the Circle
 

 

Triangle with Squares Problem

 

Thébault's Theorem. Parallelogram with Squares theorem
 

 

Varignon and Wittenbauer parallelograms. Quadrilateral: midpoints and trisection points of the edges.

 

 

Van Aubel

Van Aubel's Theorem. Quadrilateral with Squares. Proof with animation.
 

 

Equilic Quadrilateral.
 

 

Ptolemy's Theorem.
 

 

Cyclic Quadrilateral: Ratio of the Diagonals
 

 

Brahmagupta's Theorem Cyclic quadrilateral.

 

Brahmagupta's Corollary Cyclic quadrilateral.

 

Brahmagupta's Formula  Area of a cyclic quadrilateral.

 

Brahmagupta Formula Extension Area of any quadrilateral.

 

Newton's Theorem: Newton's Line. Circumscribed quadrilateral, midpoints of diagonals, center of the circle inscribed.

Puzzle of the Newton's Theorem: 50 pieces of circles.

 

Sangaku Problem. The incenters of four triangles in a cyclic quadrilateral form a rectangle.

 

Complete Quadrilateral Theorems

Presentation: "Animated Angle to Geometry Study I & II." 46th Annual Georgia Mathematics Conference, Extreme Makeover: Mathematics Edition!, Rock Eagle, October 20-22, 2005,

 

Kurschak's Tile and Theorem. Jozsef Kurschak (Hungary, 1864-1933) An elegant and a purely geometric way of finding the area of a regular dodecagon.
 

 

Proposed Problem 33.
Triangle and quadrilateral.

 

Proposed Problem 35.
Incenters and Inradii in Cyclic Quadrilateral.

 

Proposed Problem 42. Angles and triangles.

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Last updated: May 7, 2009