Online Geometry: Cyclic Quadrilateral Theorems
and Problems Table of Content 1




Ptolemy's Theorems and Problems  Index. 

Brahmagupta Theorem and Problems  Index
Brahmagupta (598–668) was an Indian mathematician and astronomer who discovered a neat formula for the area of a cyclic quadrilateral. 

Brahmagupta's Theorem
Cyclic quadrilateral.


Cyclic Quadrilateral with Perpendicular Diagonals.


Geometry Problem 1306.
Cyclic, Inscribed Quadrilateral, Circle, Tangent, Diagonals, Collinear Points. 

Geometry Problem 1271.
Triangle, Incircle, Incenter, Excircle, Excenter, Escribed Circle, Tangency Points, Six Concyclic Points. 

Geometry Problem 1268.
Triangle, Exterior Angle Bisector, Circumcircle, Circle, Chord, Parallel, Concyclic Points, Cyclic Quadrilateral. 

Geometry Problem 1261.
Cyclic Quadrilateral, Circle, Diameter, Midpoint, Measurement. 

Geometry Problem 1258.
Cyclic Quadrilateral, Concyclic Points, Measurement. 

Geometry Problem 1254.
Circle, Arc, Chord, Midpoint, Cyclic Quadrilateral, Concyclic Points. 

Geometry Problem 1250.
Cyclic or Inscribed Quadrilateral, Circle, Diameter, Congruence. 

Geometry Problem 1249.
Cyclic Quadrilateral, Circle, Triangle, Circumcircle, Angle Bisector, Parallel Lines, Area. 

Geometry Problem 1245.
Cyclic or Inscribed Quadrilateral, Circle, Arc, Midpoint, Measurement. Mobile Apps. 

Geometry Problem 1241.
Quadrilateral, Four Exterior Angle Bisectors, Cyclic Quadrilateral, Circle. Mobile Apps. 

Geometry Problem 1234
Quadrilateral, 60 Degrees, Midpoint, Congruence, Cyclic Quadrilateral, Concyclic Points. 

Geometry Problem 1227
Triangle, Circumcircle, Angle Bisector, Concyclic Points, Cyclic Quadrilateral. 

Geometry Problem 1217
Triangle, Circle, Excenter, Incenter, Angle Bisector, Cyclic Quadrilateral, Circumcircle, Tangent Line. 

Geometry Problem 1213
Triangle, Circumcircle, Altitudes, Cyclic Quadrilateral, Congruence. 

Geometry Problem 1181
Cyclic Quadrilateral and Tangential Quadrilateral, Diameter as a Diagonal, Incenter, Circumcenter. 

Geometry Problem 1176
Cyclic Quadrilateral, Diagonals, Six Diameters, Circles, Collinear Points, Concurrent Lines. 

Geometry Problem 1172
Cyclic Quadrilateral, Circle, Secant, Triangle, Similarity, Metric Relations. 

Geometry Problem 1163.
Isosceles Triangle, Congruence, Double Angle, Circle, Concyclic Points, Circumcenter, Perpendicular, Angle Bisector. 

Geometry Problem 1142.
Cyclic Quadrilateral, Isogonal Lines, Circle, Center, Radius, Perpendicular Bisector, Circumcenter. 

Geometry Problem 1130.
Cyclic Quadrilateral, Diagonals, Angle Bisector, Congruent Angles. 

Geometry Problem
1118.
Right Triangle, Angle Trisection, Concyclic Points, Cyclic Quadrilateral. 

Geometry Problem
1113.
Triangle, Perpendicular Bisector, 90 Degrees, Circle, Concyclic Points, Cyclic Quadrilateral. 

Geometry Problem 756: Four Circles Theorem
Using TracenPoche Interactive Dynamic Software.
StepbyStep construction, Manipulation, and animation. 

iPad Apps: Geometry Designer Illustration. Four Circles Theorem.
Interactive Geometry Software for iPad, iPhone, iPod. 

Ptolemy's Theorem.
Cyclic quadrilateral 

Cyclic
Quadrilateral: Ratio of the Diagonals


Brahmagupta's Corollary
Cyclic quadrilateral.


Brahmagupta's Formula
Area of a cyclic quadrilateral.


Brahmagupta Formula
Extension
Area of any quadrilateral.


Angle between two
Simson Lines. Proof with animation.


Simson Line. A proof
of Simson line with animation. 

Interactive Simson
Line. Dynamic Geometry.
StepbyStep construction, Manipulation, and animation. 

Miquel's Pentagram Theorem
Interactive proof with animation and key theorems.
Pentagons and Cyclic quadrilateral. 

Miquel's
Pentagram with Dynamic Geometry. You can alter the pentagram
dynamically in order to test and prove (or disproved) conjectures and
gain mathematical insight that is less readily available with static
drawings by hand. Requires Java Plugin 1.3 or higher. Please
be patient while the applet loads on your computer. 

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

EightPoint Circle Theorem
StepbyStep construction, Manipulation, and animation. 

Complete Quadrilateral: OrtholineSteiner Line.
Using TracenPoche Dynamic Software
StepbyStep construction, Manipulation, and animation 
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