| December 30 |
Line IO in Bicentric Quadrilaterals |
| December 29 |
Equal Angles in Two Circles II |
| December 25 |
Hippocrates' Squaring of Lunes |
| December 15 |
Quadrature: A Child's Play |
| December 13 |
Hippocrates' Squaring of a Lune |
| December 11 |
Squaring a Rectangle |
| December 10 |
Shearing a Polygon into a Triangle of Equal Area |
| November 24 |
Proof 72 of the Pythagorean Theorem |
| November 22 |
Pythagorean Theorem: Subtle Dangers of Visual Proof |
| November 20 |
Proof 71 of the Pythagorean Theorem |
| November 19 |
Cherchez le quadrilatère cyclique II |
| November 18 |
Altitudes and the Power of a Point |
| November 17 |
Use of Homogeneous Coordinates for Geometrical Calculations, by R. F. Housholder |
| November 15 |
Proof 70 of the Pythagorean Theorem |
| November 9 |
Orthodiagonal and Cyclic Quadrilaterals |
| November 8 |
Circumcenter on Angle Bisector |
| November 7 |
Projections on Internal and External Angle Bisectors |
| November 6 |
Dissection of Cyclic Quadrilateral |
| November 5 |
Orthocentric System From Rectangle |
| November 3 |
In the Wasan Spirit |
| November 2 |
Equilateral Triangles On Sides of a Parallelogram II |
| November 1 |
What Is Angle? |
| October 27 |
An Arithmetic Magic Trick |
| October 26 |
Finding Circle Center By Ruler Alone |
| October 26 |
Cherchez le quadrilatère cyclique |
| October 25 |
Equal Angles in Two Circles |
| October 24 |
Tangents, Perpendiculars and Geometric Mean |
| October 22 |
Why 17? |
| October 19 |
Angle: An Illustrated Classification |
| October 17 |
A Circle Related to Incenter and Circumcenter |
| October 16 |
Ramsey's Theorem |
| October 15 |
Property of the Line IO: a proof from the Book |
| October 10 |
Inscriptible Quadrilateral: An Illustration |
| October 10 |
When A Quadrilateral Is Inscriptible? |
| October 9 |
Egyptian Triangle By Paper Folding |
| October 9 |
A Problem on an Icy Cone |
| October 8 |
Common Chord and a Tangent |
| October 7 |
Sangaku and The Egyptian Triangle |
| October 5 |
Orthocenters of Two Triangles Sharing Circumcenter and Base |
| October 3 |
Combinatorial Proofs |
| October 1 |
Dividing Evenly a Quadrilateral II |
| September 29 |
Lucas' Theorem |
| September 28 |
Area of the Union of Two Squares |
| September 27 |
Dividing Evenly a Quadrilateral |
| September 26 |
Golden Ratio in Geometry |
| September 25 |
Classification of Quadrilaterals |
| September 24 |
Parallel Lines in a Quadrilateral |
| September 23 |
Impossible Frame |
| September 22 |
Triangle Classification |
| September 21 |
What Is Proof? |
| September 18 |
The SSA |
| September 17 |
The SSS |
| September 16 |
Expanded the page on Irrationality of sqrt(2) with introduction and two more proofs |
| September 15 |
Geometric Meaning of the Geometric Mean |
| September 14 |
Geometric Mean Sangaku |
| September 11 |
Morley's Theorem, G. Zsolt Kiss' proof |
| September 10 |
Circle Concurrency and Spiral Similarity |
| September 9 |
Two Quadruplets of Tangent Circles |
| September 8 |
Review of Kiselev's Geometry |
| September 6 |
Two Circumcircles And Two Pairs of Parallels |
| September 4 |
Pythagoras' Theorem Solely By Sliding |
| August 22 |
Orthogonality in Isosceles Triangles |
| August 21 |
Foot of Altitude and Minimum Distance |
| August 20 |
An inequality: 1 + 2-2 + 3-2 + 4-2 + ... + n-2 < 2. |
| August 19 |
Ian McGee's Observation |
| August 18 |
A Median in Touching Circles |
| August 16 |
Midpoints from Gergonne Triangle |
| August 15 |
Five Incircles in a Square |
| August 14 |
A Sangaku: Two Unrelated Circles |
| August 12 |
Chords, Concurrency and Orthic Triangle |
| August 10 |
Van Schooten's and Pompeiu's Theorems |
| August 9 |
Harmonic Ratio in Complex Domain |
| August 6 |
A Sangaku Follow-Up on an Archimedes' Lemma |
| August 5 |
A Property of the Line IO: A Bundled Statement and Proof |
| August 4 |
A Property of the Line IO |
| August 3 |
Three Parallels in a Triangle |
| August 1 |
Angle Bisector in Touching Circles |
| July 31 |
Discovery of Duane DeTemple |
| July 30 |
Two Circumcircles in Triangle |
| July 27 |
Right Isosceles Triangles on Sides of a Quadrilateral |
| July 26 |
Rotations in Disguise |
| July 25 |
Toothpick Construction of a Square |
| July 22 |
Fagnano's Problem, Izvolsky's Solution |
| July 21 |
Antiparallel |
| July 21 |
Nagel's Theorem |
| July 20 |
Two Circles on a Side of a Triangle |
| July 18 |
Shuttle Puzzle Practice |
| July 16 |
Permutations as a Product of Transpositions |
| July 14 |
Radius and Construction of a Mixtilinear Circle |
| July 13 |
Tromino as a Rep-tile |
| July 12 |
Mixtilinear Circles and Concurrence |
| July 7 |
Secant, Tangents and Orthogonality |
| July 6 |
60° Breeds 90° |
| July 5 |
Triangle Areas in a Parallelogram II |
| June 26 |
Triangle Areas in a Parallelogram |
| June 25 |
Parallelogram and Similar Triangles |
| June 22 |
Joachimsthal's Notations |
| June 21 |
Urquhart's Theorem |
| June 21 |
Reviewed the outstanding The 15 Puzzle |
| June 20 |
Kürschak's Tile and Theorem |
| June 18 |
Started the Book Reviews section |
| June 17 |
MathPro Logo |
| June 16 |
Stones in Cups |
| June 14 |
Product of permutations |
| June 13 |
Recombining Permutations |
| June 11 |
Shearing and Translation in Pythagorean Pants |
| June 10 |
Pythagoras' Theorem By Sheer Shearing |
| June 9 |
Proof 69 of the Pythagorean theorem |
| June 7 |
Integer roots of integers are irrational by S. Brodie |
| June 6 |
Coloring a Graph |
| June 5 |
Parallelogram Law: A PWW |
| June 5 |
Parallelogram Law: A Tessellation |
| June 3 |
The Law of Cosines: An Unfolded Variant |
| June 2 |
The Law of Cosines: a proof without words |
| May 14 |
Proof 68 of the Pythagorean theorem |
| May 14 |
Parallelogram Law |
| May 13 |
Proof 67 of the Pythagorean theorem |
| May 12 |
Secant Angles II |
| May 11 |
Broken Chord Theorem: S. Anderson's proof |
| May 10 |
The Cleavance Center |
| May 10 |
The Cleaver |
| May 9 |
Broken Chord Theorem by Paper Folding |
| May 8 |
Broken Chord Theorem: Patruno's proof |
| May 7 |
Broken Chord Theorem |
| May 6 |
Angle Subtended by a Diameter |
| April 29 |
Graph of a Polynomial Defined by Its Roots |
| April 28 |
Graph of a Polynomial |
| April 27 |
The ass and the mule |
| April 26 |
Midpoints of the Lines Joining In- and Excenters |
| April 25 |
Pedoe's Theorem |
| April 24 |
Proof 14 of the Butterfly theorem |
| April 24 |
ISBN Encoding |
| April 23 |
Barcode and EAN-13 Encodings |
| April 22 |
Barcode Magic |
| April 21 |
Universal Product Code |
| April 12 |
Construction of the Angle Bisector |
| April 11 |
Existence of the Circumcenter |
| April 10 |
Perpendicular Bisector |
| April 7 |
Three Touching Circles |
| April 6 |
Two Touching Circles |
| April 3 |
Proofs 65 and 66 of the Pythagorean theorem |
| March 29 |
Pythagoras' Theorem By Similarity |
| March 29 |
Proof #4 of the Eyeball Theorem |
| March 29 |
Proof #8 of Irrationality of sqrt(2) |
| March 28 |
Equidecomposition of a Triangle and a Rectangle II |
| March 27 |
Square in a Right Triangle and its fill-it-in outline solution |
| March 23 |
Billy is twice as old as Sally and other Outline Mathematics |
| March 21 |
Areas and Centroid in a Triangle |
| March 18 |
Proof 64 of the Pythagorean theorem |
| March 18 |
Proof 63 of the Pythagorean theorem |
| March 17 |
Symmedian in a Right Triangle |
| March 16 |
Proof 62 of the Pythagorean theorem |
| March 16 |
Pennies in Boxes |
| March 11 |
Mirror on the Wall |
| March 10 |
Math Telepathy |
| March 9 |
Rhind Papyrus |
| March 8 |
Peasant Multiplication |
| March 3 |
Proofs 59, 60, 61 of the Pythagorean theorem |
| February 28 |
Started a page on False Proofs of the Pythagorean Theorem |
| February 28 |
Proofs 56, 57, 58 of the Pythagorean theorem |
| February 27 |
A Problem In an Isosceles Right Triangle |
| February 26 |
Equal Areas In Parallelogram à la Pythagoras |
| February 25 |
Two Homotheties in a Parallelogram |
| February 22 |
3-Color Tower of Hanoi (Algorithm) |
| February 21 |
Another Sticky Problem II |
| February 19 |
Four Turtles (or Bugs, or Dogs, etc.) |
| February 17 |
Bottles in a Wine Rack: Proofs and Generalizations |
| February 15 |
Angles in Triangle Add to 180° |
| February 15 |
Rendezvous |
| February 12 |
Two Symmetric Triangles Are Directly Equidecomposable IV |
| February 9 |
Solution to the Four Travelers Problem by Rob Fatland |
| February 8 |
Two Symmetric Triangles Are Directly Equidecomposable III |
| February 7 |
Two Symmetric Triangles Are Directly Equidecomposable II |
| February 7 |
Two Symmetric Triangles Are Directly Equidecomposable |
| February 6 |
Angles in Triangle Add to 180° |
| February 4 |
Distance From a Point to a Straight Line |
| February 1 |
Tangent Circles and an Isosceles Triangle, a Solution |
| January 31 |
Radius of a Circle by Paper Folding |
| January 31 |
Bottema Shatters Japan's Seclusion |
| January 30 |
Tangent Circles and an Isosceles Triangle |
| January 29 |
Pythagoras and Vecten Break Japan's Isolation |
| January 26 |
Evolution of a Solution |
| January 25 |
Triangles, Squares and Areas from Temple Geometry |
| January 24 |
Universal Coloring |
| January 23 |
No Equilateral Triangles, Please |
| January 22 |
Triangle Sliding on Two Straight Lines |
| January 21 |
Bottles in a Slanted Rack |
| January 18 |
First Geometric Interpretation of Complex Numbers |
| January 12 |
Around the Incircle in a Polygon |
| January 11 |
Crossed-Lines Construction of Shapes of Constant Width |
| January 9 |
Around the Incircle |
| January 8 |
Algebraic Structure of Complex Numbers |
| January 4 |
Three Concurrent Circles |
| January 3 |
Circles And Parallels |
| January 3 |
Proof #13 of the Butterfly Theorem |
| January 3 |
Carpets in a Quadrilateral |
| January 2 |
Two Circles and a Limit |
