**Dynamic Geometry Sketches**

**(Interactive dynamic geometry sketches with JavaSketchpad**

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This site has interactive Java sketches which demonstrate several famous and beautiful theorems in mathematics such as Napoleon, Viviani, nine-point circle, Euler line, Neuberg, Van Aubel, Spieker circle, Fermat-Torricelli points, etc., as well as further generalizations of many of these. It also includes Student Explorations which contain mostly geometric problems, challenges, explorations, and classroom material of interest hopefully to both students and teachers of mathematics in school as well as undergraduate level at university such as the hierarchical classification of quadrilaterals, interior angle sum of polygons, etc. Some of the explorations are directly related to the school math curriculum such as the "classifying, exploring and defining quadrilaterals" activity, while others such as "Bottema's theorem" are intended as challenges to extend students and teachers a little beyond the usual confines of the school. Some challenges are more suitable for training of enthusiasts of mathematical competitions.

**Michael de Villiers**

**(Last Update: 23 Jan 2018)**

Visit p. 4 of my homepage for downloadable articles *Downloadable articles on Math & Math Ed*

Circumcyclicquad

A proof of the result above, a generalization as well as an interesting dual, and much more,

can be found in my book, available in bound form or downloadable PDF *Some Adventures in Euclidean Geometry*

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Get 10% off print books plus free mail till 23 July 2018 **Downloadable PDF papers/books on Geometry, Mathematics & Mathematics Education for sale**

NEW! **Problem solving and logical thinking games for young children ** Contact __dynamic learn @mweb. co. za__ (without the spaces) to order.

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**Explorations for
Students ** *( Updated)*

**Affine Equivalence of Cubic Polynomials**

**Area Ratios of Octagons/Parallelograms: IMTS problem**

**Balancing Quadrilaterals Theorem: A 'Van Aubel-like' result*** *

(An application of centroids - centres of mass)

**British Mathematics Olympiad Problem and its Dual**

(An application of perpendicular and angle bisectors of a triangle)

**Circumcentres (or Perpendicular Bisectors) of Circumscribed Quadrilateral Theorem**

**Clough's Theorem (a variation of Viviani) and some Generalizations**

**Concurrency and Euler line locus result**

**Cyclic Quadrilateral Incentre-Rectangle**

**Cyclic Quadrilateral Rectangle Result**

**De Villiers points and hyperbola of a triangle**

**Du Plooy's generalization of the Theorem of Pythagoras **

**Fermat-Torricelli Point Generalizations **

**Feynman's Triangle and some generalizations **

**Flashback to the Past - a 1949 Matric Geometry Exam Question **

**Generalizations of
Cross's (Vecten's) Theorem **

**Generalization of Euclid Book III, proposition 22 (cyclic quadrilateral theorem), and its dual**

**A generalization of
Neuberg's Theorem and the Simson line **

**2D Generalizations of
Viviani's Theorem**

3D Generalizations of
Viviani's Theorem

**2D Generalizations of a theorem of Sylvester**

Sylvester's theorem for a tetrahedron

**Generalizing a theorem of Arsalan Wares**

**Generalizing the Nagel line to Circumscribed Polygons by Analogy & Constructive Defining**

**A generalization of a Parallelogram Theorem to Parallelo-hexagons, and Douglas' Theorem**

**Haag Hexagon and its generalization to a Haag Polygon**

**Haruki's Theorem (Three Overlapping Circles)**

**A Hierarchical Classification of Quadrilaterals **

(Inclusive Classification of Quadrilaterals)

**Interior Angle Sum of Polygons (incl. Crossed): a General Formula**

**Investigating incentres of some iterated triangles **

**Locus Problem (fixed chords in circle)**

**Napoleon's Theorem and some Generalizations & Variations**

** **

**Nine-point (or Euler) centre & Maltitudes of Cyclic Quadrilateral**

** **

**Nine Point Circle and Spieker Circle Duality** *(NEW!)*

** **

**Nine-point conic and
Euler line generalization***(Updated!)*

** **

**Octagon
Centroids forming Parallelo-octagon: A Varignon Generalization**

(A generalization of Varignon's Theorem to 2D and 3D)

** **

**Para-Hexagon Concurrency Theorem**

(A generalization of concurrency of triangle medians) *(Updated!)*

** **

**Pirate Treasure Hunt and a Generalization**

** **

** **

**Quadrilateral Similar-Triangles Collinearity Theorem**

**The quasi-circumcentre and quasi-incentre of a quadrilateral**

**The quasi-Euler line of a quadrilateral and a hexagon**

**Semi-regular Angle-gons and Side-gons (A generalization of rectangles and rhombi) **

**Some Parallelo-hexagon Area Ratios**

** **

**Spieker conic and Nagel line generalization***(Updated!)*

**Trisection concurrency: a variation on a median theme**

**Van Aubel's Theorem and some Generalizations**

**A variation of Miquel's theorem and its generalization**

**Other Activities and Links**

*Cut-the-Knot - Interactive Mathematics Miscellany and Puzzles*

*Dynamically Explore Elliptic (Spherical) Geometry*

*Dynamically Explore Hyperbolic Geometry*

*Logic, Strategy & Geometry Games*

** LOGO (Turtle) Geometry Online** or download

*Mathematics Archives - Topics in Mathematics - Geometry*

*Math Forum Electronic Newsletter*

*The Importance of Geometric Literacy in Engineering & Design*

*Wolfram Alpha Online Computational Knowledge Engine*

*Homepage of Yutaka Nishiyama with several interesting mathematical applications*

*List of online resources for math teachers*

By Michael de Villiers at: prof md @ mweb .co.za (use without spaces in between)

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