.

Quadrilaterals: Theorems and Problems
The Incas built their windows and doors in the shape of trapezoids, as this shape is known for its ability to withstand earthquakes well.


Four lines intersect,
Sides, angles, shapes perplex,
Quadrilateral quests. 

Parallelograms Index.


Word Cloud of Quadrilateral.
Visual Summary. 

Square. 

Area of a Square Index.


Rectangle. Theorems and Problems Index. 

Rhombus.


Trapezoids.


Median of a Trapezoid, Theorems and Problems.
Index.


Cyclic Quadrilateral.


Tangential or Circumscribed Quadrilateral


Kite Index.


Complete Quadrilateral Index.


Equilic Quadrilateral.


Triangle and Squares. 21 theorems. Visual
illustrations. 

van Aubel's Theorem.
Quadrilateral with Squares. Proof with animation for Tablets, iPad,
Nexus, Galaxy. 

Golden Rectangles. 

Ptolemy's Theorem.


Tangential or Circumscribed Quadrilateral: Diagonals, Inradii Theorem. 

Tangential or Circumscribed Quadrilateral: Pitot Theorem. 

Geometry Problem 1543: Calculating the Area of Quadrilateral ABED in a Square with a Side Length of 20 and an Intersecting Arc. 

Geometry Problem 1538: Unlocking the Secrets of Triangular Geometry: Solve for the Area of a Quadrilateral Using External Squares and a Segment Length. 

Geometry Problem 1537 Challenge: Can You Solve for the Missing Area in a Parallelogram using Midpoints and Intersection Points?. 

Geometry
Problem 1536: Discover the Power of Midpoints: Solving for Missing Areas in Quadrilaterals. 

Geometry
Problem 1508.
Understanding Triangle Geometry: Isosceles, Equilateral, Quadrilateral, Angular. Difficulty Level: High School. 

Geometry
Problem 1502.
Right Triangle, Incircle, Inradius, Geometric Mean of 2 Inradii, Angle Bisector, Perpendicular, Tangential Quadrilateral. 

Geometry
Problem 1501.
Square, Exterior Point, Congruent Angles, Segment, Measurement. 

Dynamic Geometry 1481.
Five Tangential or Circumscribed Quadrilaterals, Pitot Theorem, Congruence, Stepbystep Illustration. GeoGebra,
iPad. 

Dynamic Geometry 1470.
Tangential Quadrilateral, Incircles, Tangent,
Parallel, Rhombus, Stepbystep Illustration. 

Geometry Problem 1467.
Square, Rectangle, Triangle, Area. 

Geometry Problem 1466.
Tangential Quadrilateral, Newton Line, Incenter, Midpoint, Diagonal, Collinear Points.
Stepbystep Illustration using GeoGebra. 

Geometry Problem 1465.
Tangential Quadrilateral, Incenter, Inscribed Circle, Equal Sum of Areas.
Stepbystep Illustration using GeoGebra. 

Geometry Problem 1464.
Quadrilateral, Interior Point, Midpoint of Sides, Equal Sum of Areas.
Stepbystep Illustration using GeoGebra. 

Geometry Problem 1463.
Parallelogram, Interior Point, Opposite Triangles with Equal Sum of Areas.
Stepbystep Illustration using GeoGebra. 

Geometry Problem 1462.
NewtonLine, NewtonGauss Line, Complete Quadrilateral, Midpoints of Sides and Diagonals,
Collinear Points. 

Geometry Problem 1461.
Quadrilateral, Triangle, Angles, 3060 Degree, Congruence, Auxiliary Lines. 

Dynamic Geometry Problem 1445.
Van Aubel's theorem, Quadrilateral and Four Squares, Centers. Stepbystep animation using GeoGebra. 

Geometry Problem 1435.
Circle, Diameter, Inscribed Circles, Circular Sector, Parallelogram, Parallel Lines, Tangency Points,
Poster, Typography, iPad Apps. 

Geometry Problem 1428. Intersecting Circles, Tangent Line, Triangle, Square, Area. 

Geometry Problem 1426. Two Squares, Collinear Points, Triangle, Quadrilateral, Sum of the Areas. 

Geometry Problem 1424. Triangle, Parallelogram, Trapezoid, Area, Diagonal, Measurement. 

Geometry Problem 1422. Triangle, Transversal, Cevian, Area,
Quadrilateral, Measurement. 

Geometry Problem 1403. Quadrilateral, 90 Degree Angle, Perpendicular, Congruence. 

Geometry Problem 1356.
Quadrilateral, Triangle, Angle, 30 Degrees, Congruence. 

Problem 1334. Square, Kite, Sum of Segments.


Geometry Problem 1324.
Quadrilateral, Diagonal, 45 Degrees, Angle Bisector, Isosceles Triangle, Congruence. 

Geometry Problem 1308.
Quadrilateral, Diagonal, Triangle, Incircle, Tangent Line, Sides, Measurement. 

Geometry Problem 1286.
Triangle, Quadrilateral, 60, 135, 105 Degree Angles, Congruence, Measurement. 

Geometry Problem 1285.
Triangle, Quadrilateral, 60, 150, 90 Degree Angles, Congruence, Measurement. 

Geometry Problem 1280.
Quadrilateral, Perpendicular Diagonals, Isosceles Right Triangles, 45 Degrees, Collinear Points. 

Geometry Problem 1267.
Triangle, Incircle, Excircle, Circle, Tangency Points, Perpendicular, 90 Degrees, Parallelogram. 

Geometry Problem 1256.
Parallelogram, Angle Bisector, Measurement. 

Geometry Problem 1243.
Quadrilateral, Four Exterior Angle Bisectors, Semisum, Angles. Mobile Apps. 

Geometry Problem 1242.
Quadrilateral, Four Interior and Exterior Angle Bisectors, Collinearity, Concurrent Lines. 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 1230
Quadrilateral, 60 Degrees, Congruence, Metric Relations. 

Geometry Problem 1226
Quadrilateral, Squares, Centers, Midpoints, Congruence. 

Geometry Problem 1203
Right Triangle, Square, Angle Bisector, Three Congruent Quadrilaterals. 

Geometry Problem 1198
Right Triangle, Square, Rectangle, Quadrilateral, Altitude, Equal Areas. 

Geometry Problem 1192
Trapezoid, Triangle, Diagonal, Midpoint, Area, Parallel. 

Geometry Problem 1188
Triangle, Parallelogram, Parallel Lines, Trapezoid, Area. 

Geometry Problem 1187
Triangle, Quadrilateral, Midpoints, Area. 

Geometry Problem 1186
Right Triangle, Square, Inscribed Circle, Tangent, Quadrilateral, Area. 

Geometry Problem 1185
Similar Rectangles, Four Quadrilaterals, Sum of the Areas, Metric Relations. 
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