Dec 29 
Three Circles and Area 
Dec 29 
Is X a Midpoint of a Chord 
Dec 27 
Proportions and the Incenter 
Dec 25 
Limit of a Recursive Sequence 
Dec 23 
An Inequality with Constraint VI 
Dec 21 
Pythagorean Perimeter Theorem 
Dec 21 
Generalized Carnot's theorem 
Dec 19 
Inequality with Csc And Sin 
Dec 19 
Euler Inequality in Triangle 
Dec 19 
Concurrence on Angle Bisector 
Dec 18 
An Inequality with Constraint V 
Dec 18 
Jensen's Inequality 
Dec 17 
An Inequality with Constraint IV 
Dec 16 
An Inequality from Morocco 
Dec 16 
An Inequality from Morocco, with a Proof, or Is It? 
Dec 15 
A Limit of Another Sequence 
Dec 14 
A Limit of a Sequence 
Dec 13 
Optimization in Parallelepiped 
Dec 12 
Dao's Variant of Thebault's First Problem 
Dec 11 
Jordan Curve Theorem 
Dec 9 
An Inequality with Constraint III 
Dec 8 
Solution #10 to a variant of the 808020 triangle problem 
Dec 8 
Solution #9 to a variant of the 808020 triangle problem 
Dec 8 
Solution #8 to a variant of the 808020 triangle problem 
Dec 7 
A Problem with Two Isosceles Triangles 
Dec 4 
Advancing a Millenium Problem 
Dec 4 
An Inequality with Constraints II 
Dec 3 
An Inequality with Constraint 
Nov 30 
Review of Problems for Metagrobologists by David Singmaster 
Nov 29 
Steiner's Circumellipse in Barycentric Coordinates 
Nov 28 
Steiner's Inellipse in Barycentric Coordinates 
Nov 27 
Area of the Intersection of Two Equal Rectangles 
Nov 26 
Pedal Parallelogram 
Nov 26 
Cevian Parallelogram 
Nov 24 
Constrained Area in Triangle 
Nov 24 
Area of Cutoff Triangles 
Nov 24 
Area of Cevian Triangle 
Nov 24 
Area Inequalities in Triangle 
Nov 22 
Inequality from Math Phenomenon 
Nov 22 
Chebyshev Inequality 
Nov 21 
Rearrangement Inequality 
Nov 19 
Sanchez's Viviani's Area Analogue 
Nov 19 
Equal areas In Circle 
Nov 18 
A Problem with Right Isosceles Triangles 
Nov 17 
Bicubal Domino 
Nov 16 
Constrained Intermarriages 
Nov 15 
Bisectors and Proportions 
Nov 10 
Newton's and Maclaurin's Inequalities 
Nov 9 
Getting Your Rightful Share Back 
Nov 6 
An Inequality from Tibet 
Nov 4 
Application of CauchySchwarz Inequality 
Nov 3 
Optimal Quadrilateral Inscribed in Square, PWW 
Nov 2 
Optimal Quadrilateral Inscribed in Square 
Oct 29 
Simple But Uncommon Equation from 1968 IMO 
Oct 29 
A Functional Equation from 1968 IMO 
Oct 27 
Inequalities and Quadratic Forms 
Oct 27 
An Application of Schur's Inequality 
Oct 26 
Schur's Inequality 
Oct 25 
An Inequality in Determinants 
Oct 23 
Fold Square into Equilateral Triangle 
Oct 22 
Areas in Three Squares 
Oct 21 
Orthogonality in Two Squares 
Oct 19 
An Equation in Matrices 
Oct 19 
The Shortest Crease 
Oct 17 
An Equation in Integers and Rational Numbers 
Oct 16 
Pythagorean Theorem, Proof 114 
Oct 16 
Pythagorean Theorem by Inscribed Semicircle 
Oct 15 
Golden Ratio in Isosceles Right Triangle, Square, and Semicircle 
Oct 14 
Trisect Segment: 2 Circles, 4 Lines 
Oct 13 
Extremal Problem in a Quadrilateral 
Oct 11 
Centroids and Circumcenters 
Oct 9 
Butterfly in Inscriptible Quadrilateral 
Oct 8 
Prove 2[sqrt(n)  sqrt(n1)] > 1/sqrt(n) 
Oct 7 
Angles in a Triangle: an Exercise 
Oct 2 
Thales on Angle Bisectors 
Sep 25 
Angle Chasing on Radical Axis 
Sep 24 
Angle in Square 
Sep 21 
An Application of Hlawka's Inequality 
Sep 19 
Scalar Product Optimization 
Sep 17 
Tangents And Bisectors 
Sep 14 
Equation in Permutations 
Sep 12 
Triangle by HM segments 
Sep 9 
Transversal Trigonometry 
Sep 9 
A Property of Cyclic Quadrilateral 
Sep 8 
Miguel Ochoa's van Schooten is a Slanted Viviani 
Sep 8 
Miguel Ochoa's van Schooten Like Theorem III 
Sep 7 
Miguel Ochoa's van Schooten Like Theorem II 
Sep 6 
On the Intersection of 1+x and e^x and Trigonometric Consequences 
Sep 4 
A Problem of Acute Triangle 
Sep 3 
When a Triangle is Acute 
Sep 1 
Homothety in Equilateral Triangles 
Aug 31 
What 1, 6, and 14 Have to Do with 5 
Aug 30 
Concurrence in Equilateral Triangle 
Aug 28 
Inequality in Rectangle 
Aug 27 
The Dual of Maxwell's Theorem 
Aug 25 
Area of Trapezoid 
Aug 24 
Extremal Distance Ratio 
Aug 23 
An Identity in Triangle II 
Aug 5 
AlgebraicGeometric Equation 
Aug 4 
Modern Day Sangaku 
Aug 2 
Amazing Mix of Triangular Numbers and Golden Ratio 
Jul 28 
An Unusual Quadratic Equation 
Jul 27 
Regular Hexagon from Arbitrary Triangle 
Jul 26 
Inequality for Integer Sequences II 
Jul 26 
Inequality in Acute Triangle 
Jul 26 
Inequality for Integer Sequences 
Jul 25 
Perspective Triangles in Circle 
Jul 24 
Relation Engendered By Medians 
Jul 24 
Relation Engendered By Altitudes 
Jul 23 
Cubic Equation for the Sides of a Triangle 
Jul 23 
Property of Quadratic Polynomials 
Jul 22 
Pleasant Proportions in Triangle 
Jul 21 
An Inequality via Young's Theorem 
Jul 21 
An Angle Inequality in Simple Polygons 
Jul 20 
Reuleaux's Triangle, Extended 
Jul 14 
Triangle from Two Side Lines and the Euler Line 
Jul 10 
An Universal Inequality for Cevians 
Jul 1 
Iterations on Monotone Functions 
Jun 30 
Tangential Chaos 
Jun 29 
An innovative recurrence 
Jun 25 
An Equation in Determinants 
Jun 24 
Two Related Triangles of Equal Areas 
Jun 22 
Leo's Lemma, Second Application 
Jun 21 
Two Sequences Defined by Recurrence 
Jun 19 
Three visions of a fact 
Jun 17 
Simpson Paradox

Jun 17 
Importance of Having an Angle of 60 Degrees 
Jun 17 
Triangle with a 60 degrees angle 
Jun 16 
A Sum of a Double Series 
Jun 16 
Leo Giugiuc's Trigonometric Lemma 
Jun 15 
Is There a Limit 
Jun 14 
A OneLine Proof of the Infinitude of Primes 
Jun 11 
Clough's theorem: the simplest proof 
Jun 10 
Beyond Viviani 
Jun 10 
Slanted Viviani, PWW 
Jun 8 
Area Inequality in Triangle II 
Jun 7 
Slanted Viviani 
Jun 6 
YATPOPT, Yet Another Trigonometric Proof of the Pythagorean Theorem 
Jun 5 
Problem in Direct Similarity 
Jun 4 
Inverse Similarity through Reflections 
Jun 2 
An Inequality with Nested Radicals 
May 31 
From Triangle Inequality to Inequality in Triangle 
May 28 
A Curious Identity in Triangle 
May 26 
An Inequality in Triangle, II 
May 26 
The Jeweler's Observation, a look back 
May 25 
Isotomic Reciprocity 
May 20 
Construct Triangle from Altitude, Median and Inradius 
May 18 
An Affine Property of Barycenter 
May 18 
An Identity for Regular Tetrahedra 
May 16 
Van Khea's Fourth Identity in Triangle 
May 12 
Parabolas Related to the Orthic Triangle 
May 11 
An Inequality in Triangle 
May 11 
Parabolic Reciprocity 
May 10 
Miguel Ochoa's van Schooten Like Theorem 
May 10 
Elegant Minimum of a Function 
May 7 
One More Seven Circles Theorem 
May 7 
William Wallace's 1803 Statement of the Butterfly Theorem 
May 6 
Third Unusual Identity in Triangle 
May 4 
DanStefan Marinescu Inequality 
May 4 
Twin Segments in Four Semicircles 
May 2 
Characterization of Trapezoid 
May 1 
A wrapping surprise 
Apr 30 
Review of The Proof and The Pudding by Jim Henle 
Apr 28 
From Arbitrary Pentagon to Regular One 
Apr 25 
A Geometric Proof of Proizvolov's Identity 
Apr 24 
From Arbitrary Hexagon to Regular One 
Apr 22 
Extras in Bottema's Configuration 
Apr 22 
From Straight Line to Regular Hexagon 
Apr 21 
Parallelogram in Parallelogram And in Projection 
Apr 20 
A Problem in Three Pentagons 
Apr 19 
A Generalization of Simson Line 
Apr 17 
A Combinaton Locus 
Apr 16 
Golden Ratio in Mixtilinear Circles 
Apr 16 
Proofs of the Pythagorean Theorem via Heron's Formula II 
Apr 15 
Further Properties of Peculiar Circles 
Apr 14 
An Inequality from the 2015 Romanian TST 
Apr 6 
Another Identity in Triangle 
Apr 5 
Circle of Apollonius in Equilateral Triangle 
Apr 5 
Integer Triangle That Sums to Cube 
Apr 5 
Another Sangaku in Square 
Apr 3 
An Identity in Triangle 
Apr 3 
Square Roots and Triangle Inequality 
Apr 1 
Why Learn Mental Math Tricks? 
Mar 30 
Four Golden Circles 
Mar 27 
Construct Triangle by Angle, Median, and Circumradius 
Mar 27 
Two Conics, Pascal, Chasles, and CrossRatio 
Mar 26 
Construct Triangle by Angle, Altitude and Median 
Mar 24 
A Conic in a Triangle 
Mar 22 
Concurrence in Arbelos 
Mar 21 
Areas in Two Parallelograms and a Translation 
Mar 19 
Triangle from Angle Bisector, Altitude and Inradius 
Mar 19 
Triangle from Median, Altitude and Circumradius 
Mar 18 
An Equation Involving the Total Number of Digits 
Mar 16 
Triangle from Angle Bisector, Altitude and Circumradius 
Mar 16 
An Equation Involving Four Collinear Points 
Mar 16 
Hlawka's Inequality 
Mar 13 
Area Inequality in Triangle 
Mar 11 
Construct Triangle from Angle, Inradius, and Altitude 
Mar 11 
Triangle from Angle, Inradius, and Difference of Sides 
Mar 10 
Infinitude of Primes As a Quickie 
Mar 5 
Between a Cross and a Square 
Mar 4 
Infinitude of Primes Via Powers of 2 
Mar 4 
Sophie Germain's Identity 
Mar 3 
A Property of Number 4 
Mar 2 
Equilateral Triangle on a Closed Curve 