Geometry articles, theorems, problems
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Pictorial Geometry Index
- 1 + 27 = 12 + 16 Sangaku
- 120° Breeds 90° [Java]
- 3 Roads, 3 Travelers [Java]
- 3 Utilities Puzzle
- 3D Quadrilateral - a Coffin Problem
- 3-4-5 Triangle by a Kid
- 4 Travelers problem
- 6 to 9 Point Circle [Java]
- 60o Breeds 90o [Java]
- 7 = 2 + 5 Sangaku
- 9-point Circle as a Locus of Concurrency [Java]
- A better solution to a difficult sangaku problem
- A Case of Similarity [Java]
- A Chain of Touching Circles in a Polygon (a la Bui Quang Tuan) [Java]
- A Chain of Touching Circles in a Polygon (à la Evelyn) [Java]
- A Characterization of the Euler Line [Java]
- A Circle in an Isosceles triangle from the 2006 Itish MO
- A Circle Related to Incenter and Circumcenter [Java]
- A Circle Rolling in an Equilateral Triangle [Java]
- A Circle With Two Centers [Java]
- A Corrected Version of the Calculus Proof of the Pythagorean Theorem
- A Geometric Limit
- A Hard but Important Sangaku
- A Hinged Realization of a Plane Tessellation [Java]
- A Lemma of Equal Areas [Java]
- A Line in a Square Grid [Java]
- A Line in Triangle Through the Circumcenter [Java]
- A Multiplicative Identity of Areas in a Triangle [Java]
- A Note on Cavalieri's Indivisibles
- A Parallelogram in Triangle [Java]
- A Possibly First Proof of the Concurrence of Altitudes
- A Problem In an Isosceles Right Triangle [Java]
- A Problem on an Icy Cone
- A problem with equilateral triangles [Java]
- A Proof Perigal and All Others After Him Missed
- Properties of the Figures in Euclid I.47
- A Property of Equiangular Polygons [Java]
- A Property of Rhombi [Java]
- Property of Semicircles [Java]
- A Property of the Line IO [Java]
- A Property of the Line IO: A Bundled Statement and Proof [Java]
- Property of the Line IO: a proof from the Book [Java]
- A Relation in Triangle
- A Restored Sangaku
- A Sangaku Follow-Up on an Archimedes' Lemma [Java]
- A Sangaku: Two Unrelated Circles [Java]
- A Sangaku with an Egyptian Attachment [Java]
- A Sangaku with Many Circles and Some [Java]
- Semi-regular Tessellation on Hinges A [Java]
- Semi-regular Tessellation on Hinges B [Java]
- A Stronger Triangle Inequality [Java]
- A Sushi Morsel
- A Three Pegs Question [Java]
- A Triangle of Antreas Hatzipolakis [Java]
- A Trigonometric Identity in a Right Triangle from the 1960 IMO
- A Trigonometric Solution to a Difficult Sangaku Problem
- An Area Inequality
- About a Line and a Triangle [Java]
- Abul Wafa al-Buzjani's Proof of the Pythagorean Theorem [Java]
- Acute Angle Bisectors in a Right Triangle [Java]
- Adams' Circle [Java]
- Addition and Subtraction Formulas for Sine and Cosine
- Addition and Subtraction Formulas for Sine and Cosine II
- Algebraic proof of the theorem of butterflies in quadrilaterals
- All Triangles Are Isosceles [Java]
- Altitudes [Java]
- Altitudes and the Euler Line [Java]
- Altitudes and the Power of a Point [Java]
- Altitudes Concur at a Point: a Second Look
- An Extension of van Schooten's Theorem
- An Identity in a Regular Heptagon
- An Isoperimetric Theorem [Java]
- An Old Japanese Theorem
- Angle: An Illustrated Classification [Java]
- Angle Bisector in Equilateral Trapezoid
- Angle Bisector in Parallelogram [Java]
- Angle Bisectors In Rectangle [Java]
- Angle Bisector in Touching Circles [Java]
- Angle Bisectors [Java]
- Angle Bisectors and Perpendiculars in a Quadrilateral [Java]
- Angle Bisectors in Ellipse [Java]
- Angle Bisectors in Ellipse II [Java]
- Angle Bisectors in a Quadrilateral [Java]
- Angle Bisectors in a Quadrilateral - Cyclic and Otherwise [Java]
- Angle Bisectors On Circumcircle [Java]
- Angle Subtended by a Diameter [Java]
- Angle Preservation Property [Java]
- Angle Trisection, the Impossibility of Thereof
- Angle Trisection by Archimedes [Java]
- Angle Trisection by Hippocrates [Java]
- Angle Trisection by Paul Vjecsner [Java]
- Angle Trisectors on Circumcircle [Java]
- Angle Trisection by Paper Folding
- Angles in a Cube I [Java]
- Angles in a Cube II [Java]
- Angles in a Cube III [Java]
- Angles in Triangle Add to 180o
- Angles Inscribed in an Absent Circle [Java]
- Anticomplementary Triangle Surprise [Java]
- Antiparallel [Java]
- Antiparallel via Three Reflections [Java]
- APMO 1995 Problem 3
- APMO 1998, Problem 4
- APMO 2002, Problem 3
- APMO 2003, Problem 2
- APMO 2004, Problem 2
- Apollonian Circles Theorem [Java]
- Apollonian Gasket [Java]
- Apollonius Problem [Java]
- Approximate Construction of Regular Pentagon by A. Dürer
- Arbelos -- the Shoemaker's Knife [Java]
- Another Pair of Twins in an Arbelos [Java]
- Archimedes' Quadruplets [Java]
- Archimedes' Twin Circles and a Brother [Java]
- Area of an Arbelos [Java]
- Areal Butterflies
- Bisection of Yin and Yang
- Chain of Circles on a Chord [Java]
- Chain of Inscribed Circles [Java]
- Characteristic Property Of Right Triangles
- Chromatic Number of the Plane
- Concurrency in Arbelos [Java]
- Concyclic Points in Arbelos [Java]
- Rectangle in Arbelos [Java]
- Squares in Arbelos [Java]
- Twin Segments in Arbelos [Java]
- Archimedes' Book of Lemmas
- Book of Lemmas: Proposition 1 [Java]
- Book of Lemmas: Proposition 2 [Java]
- Book of Lemmas: Proposition 3 [Java]
- Book of Lemmas: Proposition 5 [Java]
- Book of Lemmas: Proposition 6 [Java]
- Book of Lemmas: Proposition 7
- Book of Lemmas: Proposition 9 [Java]
- Book of Lemmas: Proposition 10 [Java]
- Book of Lemmas: Proposition 11
- Book of Lemmas: Proposition 12 [Java]
- Book of Lemmas: Proposition 13 [Java]
- Book of Lemmas: Proposition 15
- Archimedes' Law of the Lever [Java]
- Archimedes' Method
- Archimedes' Twins in the Edo Period
- Area of a Bicentric Quadrilateral
- Area of a Circle by Leonardo da Vinci [Java]
- Area of a Circle by Rabbi Abraham bar Hiyya Hanasi [Java]
- Area of Median Triangle [Java]
- Area of Parallelogram [Java]
- Area of the Union of Two Squares [Java]
- Area of Triangle [Java]
- Areas and Centroid in a Triangle [Java]
- Areas In Circle
- Equal Areas in Regular 2n-gons [Java]
- Areas in Square by Dissection [Java]
- Arithmetic-Geometric Mean Inequality
- Arithmetic Mean Sangaku [Java]
- Arithmetic Mean Sangaku II [Java]
- Around the Incircle [Java]
- Around the Incircle in a Polygon [Java]
- Artisans vs Mathematicians
- Asian Pacific Kite [Java]
- Assigning Numbers to Points in the Plane
- Assimilation Illusion [Java]
- Asymmetric Propeller [Java]
- Asymmetric Propeller by Plane Tiling [Java]
- Axis of Similitude of Three Circles
- Barbier, The Theorem of [Java]
- Barycentric coordinates
- Bender: A Visual Illusion [Java]
- Between Major and Minor Circles [Java]
- Bevan's Point and Theorem [Java]
- Bimedians and Diagonals in a Quadrilateral
- Bimedians in a Regular Tetrahedron [Java]
- Bisectal Circle [Java]
- Bisecting arcs
- Bisecting a shape
- Bisector of an imaginary angle may be real
- Bottema Shatters Japan's Seclusion [Java]
- Bottema's theorem [Java]
- Bottles in a Wine Rack [Java]
- Bounded Distance
- Brahmagupta's Formula and Theorem
- Brahmagupta's Theorem [Java]
- Brahmagupta-Mahavira Identities
- Brianchon in Ellipse [Java]
- Brianchon's theorem [Java]
- Brick Wall Illusion [Java]
- Bride's Chair [Java]
- Brief introduction to Rational Trigonometry
- Broken Chord Theorem [Java]
- Building a Bridge [Java]
- Building Bridges [Java]
- Bulging lines illusion [Java]
- Butterfly Theorem
- A Better Butterfly Theorem
- The Lepidoptera of the Circles [Java]
- The Lepidoptera of the Quadrilateral
- Butterflies in Quadrilaterals and Elsewhere
- Pinning Butterfly on Radical Axes [Java]
- Two Butterflies Theorem [Java]
- Two Butterflies Theorem II [Java]
- Two Butterflies Theorem III [Java]
- Butterfly in Ellipse [Java]
- Butterflies in Hyperbola
- The Plain Butterfly Theorem [Java]
- Butterfly theorem, a Projective Proof
- Butterflies in Similar Co-axial Conics
- Cabart's Collinearity
- Cantor Set and Function
- Cantor's Theorem [Java]
- Carnot's Theorem
- Carnot's Theorem
- Carnot's Theorem (Generalization of Wallace's theorem) [Java]
- Carpet With a Hole [Java]
- Carpets Theorem [Java]
- Casey's Theorem [Java]
- Three Points Casey's Theorem [Java]
- centers of similitude
- Centroid, a Characteristic Property Of
- Centroids in a Polygon [Java]
- Chasing Angles in Pascal's Hexagon [Java]
- Circle, Isosceles Triangle and Fixed Point [Java]
- Circle Centers on Radical Axes [Java]
- Circle Chains on Napoleon Triangles [Java]
- Circle in a Square Inscribed in a Circle [Java]
- Circles on the sides of a triangle from the 2005 Austrian MO
- Circles Tangent to Circumcircle [Java]
- Circles with Tangent Diameters [Java]
- Ceva and Menelaus Meet on the Roads
- Ceva in Circumscribed Quadrilateral
- Ceva's Theorem
- Ceva's Theorem and Fibonacci Bamboozlement [Java]
- A Faulty Dissection [Java]
- Cevian Cradle [Java]
- Cevian Nest [Java]
- Cevian Triangle [Java]
- Chain of Inscribed Circles [Java]
- Chaos, Emergence of [Java]
- Chasles' Theorem
- Cherchez le quadrilatère cyclique [Java]
- Cherchez le quadrilatère cyclique II [Java]
- Chords, Concurrency and Orthic Triangle [Java]
- Chvatal's Art Gallery Theorem [Java]
- Circle and Hyperbola as Lighthouse Curves
- Circle and Hyperbola as Lighthouse Curves II
- Circle Crosses Triangle [Java]
- Circle Concurrency and Spiral Similarity [Java]
- Circle Division by Euclid and Leonardo [Java]
- Circle of Similitude [Java]
- Circle through the Circumcenter [Java]
- Circle through the Incenter [Java]
- Circle through the Incenter And Antiparallels [Java]
- Circle-Stacking Theorem [Java]
- Circles And Parallels [Java]
- Circles and Semicircles in Rectangle [Java]
- Circles Cover a Quadrilateral [Java]
- Circles in a Circular Segment
- Circles in a Regular Polygon [Java]
- Circles in Morley's Triangles [Java]
- Circles Lined on the Legs of a Right Triangle [Java]
- Circles On Cevians [Java]
- Circles through the Orthocenter [Java]
- Circles with Equal Collinear Chords [Java]
- Circular Poggendorff Illusion [Java]
- Circle Inscribed in a Circular Segment [Java]
- Circumcenter on Angle Bisector [Java]
- Circumcevian Triangle [Java]
- Classification of Quadrilaterals [Java]
- Cleavance Center [Java]
- Cleaver [Java]
- Clifford Algebras
- Clifford's Chain [Java]
- Coaxal Circles on Perpendicular Bisector [Java]
- Coaxal Circles Theorem [Java]
- Collage Theorem [Java]
- Collinearity in Bicentric Quadrilaterals [Java]
- Collinearity via Concyclicity [Java]
- Collinearity with the Orthocenter [Java]
- Color Cycling on the Mandelbrot Set [Java]
- Coloring Plane with Three Colors
- Coloring Points in the Plane
- Common Chord and a Tangent [Java]
- Common Tangents to Two Circles I [Java]
- Common Tangents to Two Circles II [Java]
- Complete Quadrilateral [Java]
- Complex Numbers and Geometry
- Concurrency of the Altitudes in a Triangle - Trigonometric Proof
- Concyclicity in Rectangle [Java]
- Concurrency in the Intouch Triangle [Java]
- Concyclic Circumcenters: A Dynamic View [Java]
- Concyclic Points in a Triangle
- Concyclic Points in Bride's Chair [Java]
- Concyclic Points in Equilateral Bumps [Java]
- Conic Sections
- Conic Sections as Loci of Points [Java]
- Conjugate Diameters in Ellipse [Java]
- Consecutive Isosceles Decomposition [Java]
- Constant Chord
- Constructing a triangle from its angle bisectors is in general impossible
- Construction of a Cyclic Quadrilateral
- Construction of a Square from the 2008 Austrian MO
- Construction of a Triangle from the Circumcenter, Orthocenter and Incenter
- Construction of a Triangle from Two Vertices and the Centroid
- Construction of Conics from Pascal's Theorem [Java]
- Construction of Regular Pentagon by H. W. Richmond
- Construction of the Angle Bisector [Java]
- Construction of the Perpendicular Bisector [Java]
- Construction problem [Java]
- Constructions Related To An Inaccessible Point
- Construction with the Compass Only
- Continuous Line Illusion [Java]
- Convex Polygon Is the Intersection of Half Planes [Java]
- Copernicus' Theorem [Java]
- Proof of Copernicus' Theorem [Java]
- Construction with Optimization in Angle - Problem the 1979 USA Mathematical Olympiad
- cos(36°) = (1 + √5)/4
- Cosine Law
- Counting Triangles and Segments in a Polygon [Java]
- Cross Points in a Polygon [Java]
- Cross-Ratio
- Crossed-Lines Construction of Shapes of Constant Width [Java]
- Crossing Number of a Graph
- Cube Counting Ambiguity [Java]
- Curry's Paradox [Java]
- Cut the Cone [Java]
- Cut the Cube [Java]
- Cut the Cylinder [Java]
- Cutting Squares
- Cutting Triangles off Regular Hexagon
- Cyclic Hexagon [Java]
- Cyclic Quadrilateral, Concurrent Circles and Collinear Points [Java]
- Cycloids [Java]
- Dancing Rectangles Model Auxetic Behavior [Java]
- Dancing Squares or a Hinged Plane Tessellation [Java]
- David Richeson's Extention of an Old Japanses Theorem [Java]
- Day's Sine Illusion [Java]
- A Decomposition of Isosceles Triangles into 4 Isosecles Triangles
- Delboeuf Illusion [Java]
- Delian Problem Solved [Java]
- Desargues in the Bride's Chair (with Pythagoras)
- Desargues' Theorem [Java]
- Determination of π
- Diagonal Count [Java]
- Diagonals in a Cyclic Quadrilateral
- Diameters and Chords [Java]
- Directly Similar Figures [Java]
- Disappearing Lines puzzle [Java]
- Discovery of Duane DeTemple [Java]
- Dissection of a 10×13 Rectangle into Two Chessboards
- Dissection of a Vase [Java]
- Dissection of Cyclic Quadrilateral [Java]
- Dissection of Triangle into Rhombus [Java]
- Dissection of Triangle into Rhombus by Hubert Shutrick [Java]
- Distance
- Distance between the Orthocenter and Circumcenter
- Distance Formula
- Distorted Lines Illusion [Java]
- Divergent Spirals Illusion [Java]
- Divide a Circle into N Parts of Equal Area
- Divide a segment into n equal parts
- Dividing a Segment by Paper Folding
- Dividing a Segment into N parts: Besteman's Construction [Java]
- Dividing a Segment into N parts: Besteman's Construction II [Java]
- Dividing a Segment into N parts: GLaD Construction [Java]
- Dividing a Segment into N parts: SaRD Construction [Java]
- Al-Nayrizi's Construction [Java]
- Euclid's Segment Division [Java]
- Similar Right Triangles [Java]
- Dividing Evenly a Quadrilateral [Java]
- Dividing Evenly a Quadrilateral II [Java]
- Double Generation Theorem [Java]
- Drawing circles [Java]
- Droz-Farny Circles [Java]
- Droz-Farny Line Theorem [Java]
- Duplication of the Cube
- Dynamic Construction of Ellipse and Other Curves [Java]
- E. W. Dijkstra's Proof of the Pythagorean Theorem [Java]
- Easy Construction of Bicentric Quadrilateral [Java]
- Easy Construction of Bicentric Quadrilateral II [Java]
- Egyptian Triangle By Paper Folding
- Eight Equal Tangents [Java]
- Eight Point Circle [Java]
- Ellipse in Arbelos [Java]
- Ellipse Between Two Circles [Java]
- Equal Angles in Two Circles [Java]
- Equal Angles in Two Circles II [Java]
- Equal Areas in Equilateral Triangle [Java]
- Equal Areas In Parallelogram à la Pythagoras [Java]
- Equal Chords in Crossing Circles [Java]
- Equal Circles, Medial Triangle and Orthocenter [Java]
- Equal Incircles Theorem [Java]
- Equichordal points: Just Do It [Java]
- Equidecomposition of a Rectangle and a Square [Java]
- Equidecomposition of Two Rectangles [Java]
- Equidecomposition of a Triangle and a Rectangle [Java]
- Equidecomposition of a Triangle and a Rectangle II [Java]
- Equidecomposition of Two Parallelograms [Java]
- Equilateral and 3-4-5 Triangles [Java]
- Equilateral Triangle on Parallel Lines [Java]
- Equilateral Triangle, Straight Line and Tangent Circles [Java]
- Equilateral Triangles and Incircles in a Square
- Equilateral Triangles on Diagonals of Antiequilic Quadrilateral [Java]
- Equilateral Triangles On Sides of a Parallelogram [Java]
- Equilateral Triangles On Sides of a Parallelogram II [Java]
- Equilateral Triangles on Sides of a Quadrilateral [Java]
- Equilic Quadrilateral I, a Flawed Proof [Java]
- Equilic Quadrilateral I, A Variation [Java]
- Equilic Quadrilateral II [Java]
- Erdös-Mordell Inequality
- Escher's Theorem [Java]
- Euclid's Fifth Postulate
- Euclid's Elements Reference Page
- Euclid I.43 [Java]
- Euclid I.43 Extended [Java]
- Euclidean Construction of Center of Ellipse [Java]
- Euclidean Construction of Tangent to Ellipse
- Euler Line Cuts Off Equilateral Triangle [Java]
- Euler Line and 9-Point Circle [Java]
- Euler's Formula and Poncelet Porism
- Every Parallelogram Is a Rectangle
- Existence of the Circumcenter [Java]
- Existence of the Euler Line: An Elementary Proof [Java]
- Existence of the Incenter: a Second Look
- Experimentation with Dynamic Geometry Software: An Example [Java]
- Exterior Angle Theorem - an appreciation
- External Angle Bisector [Java]
- Extouch Triangle in Poncelet Porism [Java]
- Extremal Problem in a Circular Segment
- The Extreme Principle
- Eyeball Theorem [Java]
- Fagnano's problem [Java]
- Faulty Symmetry
- Fermat point and 9-point Centers [Java]
- Feuerbach's Theorem: A Proof [Java]
- Find a Common Chord of Given Length [Java]
- Find the Angle! [Java]
- Finding a Parallelogram in 3D
- Finding Circle Center By Ruler Alone [Java]
- Five Concyclic Points [Java]
- Five Incircles in a Square [Java]
- Five Incircles Theorem [Java]
- Fixed Point in a Kite - Problem from the 1993 Asian Pacific MO
- Fixed Point in Isosceles and Equilateral Triangles
- Fixed Point of Circles Orthogonal to the Given One [Java]
- Fixed points from 2007 Irish Mathematical Olympiad
- Fleury's Algorithm and Euler's Paths and Cycles [Java]
- Following the Hilbert Curve [Java]
- Foot of Altitude and Minimum Distance [Java]
- Focal Definition of Ellipse [Java]
- Focus and Directrix of Ellipse [Java]
- For every object there is a distance at which it looks its best.
- Ford's touching circles
- Four Centroids and Parallels [Java]
- Four Circles In a Triangle [Java]
- Four Concurrent Lines in a Cyclic Quadrilateral [Java]
- Four Construction Problems [Java]
- Four Crossing Circles [Java]
- Four Geometric Problems of Antiquity
- Four Hinged Squares [Java]
- Four Incident Circles [Java]
- Four Incircles in Equilateral Triangle [Java]
- Four 9-Point Circles in a Quadrilateral [Java]
- Four Pedal Circles [Java]
- Four Touching Circles [Java]
- Four Touching Circles II [Java]
- Four Touching Circles III [Java]
- Four Triangles, One Circle [Java]
- Four Turtles (or Bugs, or Dogs, etc.) [Java]
- Fractal curves and dimension [Java]
- Friendly Kiepert's Perspectors [Java]
- From Equilateral Triangle and Square to Golden Ratio
- From Foci to a Tangent in Ellipse [Java]
- Fundamental Theorem of 3-Bar Motion [Java]
- Fuss' Theorem [Java]
- Generalizing a Romanian Olympiad Problem [Java]
- Geometric Illustration of a Convergent Series
- Geometric Mean Sangaku
- Geometric Meaning of the Geometric Mean
- Geometric Optimization from the Asian Pacific Mathematical Olympiad [Java]
- Geometric Proofs Of the Irrationality of Square Roots
- Geometry, Algebra, and Illustrations
- Gergonne and Medial Triangles Are Orthologic [Java]
- Gergonne and Soddy Lines Are Perpendicular [Java]
- Gergonne in Ellipse [Java]
- Gergonne and Van Obel Theorems
- Gion Shrine Problem
- Given Parabola, Find Axis
- Glide Reflection [Java]
- Golden Ratio in Geometry
- Golomb's inductive proof of a tromino theorem [Java]
- Gothic Arc [Java]
- Graph Theory [Java]
- Grebe: from Ladies' Diary to Carroll's Pillow [Java]
- Grebe's Theorem
- Greg Markowsky's Problem for Parabola [Java]
- Griffiths Points in Cyclic Quadrilateral [Java]
- Griffiths' Theorem
- Half Turn, Reflection in Point [Java]
- Halving a square
- Harmonic Mean in Geometry
- Harmonic Mean Sangaku [Java]
- Harmonic Ratio
- Harmonic Ratio in Complex Domain
- Hart Circle [Java]
- Hart's Inversor [Java]
- Haruki's Lemma [Java]
- Haruki's Theorem
- Hausdorff Distance
- Hearty Munching on Cardioids [Java]
- Height/Width Interplay Illusion [Java]
- Helly's Theorem
- Hering Illusion [Java]
- Hermann Grid Illusion [Java]
- Heron's formula
- Heron's Formula: a Proof [Java]
- Heron's Problem [Java]
- Hexagon Parallel to Medial Triangle [Java]
- Hexagon Parallel to Orthic Triangle [Java]
- Hexagons in a Square
- Hinged Greek Cross Tessellation [Java]
- Hinged Squares [Java]
- Hippocrates' Squaring of a Lune [Java]
- Hippocrates' Squaring of Lunes
- Hjelmslev Theorem [Java]
- Homologous Lines under Three Spiral Similarities [Java]
- Homothety [Java]
- Homothety between In- and Excircles [Java]
- Hooper's Paradox [Java]
- How Fast Does One's Shadow Grow?
- Hunting Right Angles [Java]
- Ian McGee's Observation [Java]
- IMO 1998 Problem 1
- IMO 2004, Problem 5
- IMO 2006, Problem 1
- Impossible Fork [Java]
- Impossible Frame [Java]
- Importance of Occluders: Motion Binding [Java]
- In the Wasan Spirit
- Incenters in Cyclic Quadrilateral [Java]
- Incidence in Feuerbach's Theorem [Java]
- Infinitude of Primes - A Topological Proof
- Inscribed and Central Angles in a Circle [Java]
- Inscribed Angles [Java]
- Inscriptible and Exscriptible Quadrilaterals [Java]
- Inscriptible Quadrilateral: An Illustration [Java]
- Internal Tangents to Three Circles [Java]
- Intersecting Chords Theorem
- Intersections of a Circle with the Four Quadrants [Java]
- Intouch Triangle in Poncelet Porism [Java]
- Invariance in Orthodiagonal Quadrilaterals [Java]
- Invariant Area Sweep Implies Pythagorean Theorem [Java]
- Inversion: Reflection in a Circle [Java]
- Inversion [Java]
- Inversion in the Incircle [Java]
- Inversion Tool
- Inversion with Negative Power [Java]
- Involution on the Projective Line
- Is Every Trapezoid Parallelogram? [Java]
- Isosceles Tetrahedron
- Isogonal and Isotomic Conjugalities [Java]
- Isogonal Concurrency [Java]
- Isogonal image of the circumcircle [Java]
- Isoperimetric Theorem and Inequality
- Isosceles on the Sides of a Triangle [Java]
- Isotomy and Isogonality Hand-in-Hand [Java]
- Iterations and the Mandelbrot Set [Java]
- Iterations on a Circle Through Three Points [Java]
- Iterations on Euler Lines [Java]
- J. Casey's Additions to Euclid I.47
- Jan Stevens' proof of E. W. Dijkstra's Generalization of the Pythagorean theorem
- Joachimsthal's Notations
- John Sharp's Paradox [Java]
- Johnson Circles [Java]
- Join Circles by Given Segment [Java]
- Joseph Keech in Bride's Chair [Java]
- Judd Illusion [Java]
- Julia sets indexing [Java]
- Kanizsa Triangle [Java]
- Kiepert's Theorem [Java]
- Knots [avi movie]
- Knots on a Torus [Java]
- Kürschak's Tile and Theorem [Java]
- La Hire's Theorem [Java]
- La Hire's Theorem [Java]
- La Hire's Theorem in Ellipse [Java]
- Langman's Paradox [Java]
- Lean Napoleon's Triangles [Java]
- Length of the diagonal of the unit square equals the square root of 2
- Lennes' Polyhedron [Java]
- Lepidoptera of the Circles [Java]
- Line IO in Bicentric Quadrilaterals
- Line through a Point in an Angle
- Line, Circle, and Fixed Points [Java]
- Loci of points in a cube
- Locus of Points in a Given Ratio to Two Points [Java]
- Longest segment
- Mach's Conservation of Area and the Pythagorean Theorem
- MacLaurin's Construction of Conics [Java]
- Maimed Cake [Java]
- Malfatti's Problem [Java]
- Malfatti's Problem, Hart's Solution [Java]
- Mascheroni Construction of a Regular Pentagon
- Mathematical Droodles [Java]
- Mathematics in Pizzeria [Java]
- MathPro Logo [Java]
- Maximal Properties of the Pythagorean Relation
- Maximum Area Property of Equilateral Triangles
- Maximum Area Property of the Medial Triangle
- Maximum Perimeter Property of the Incircle {*}
- Maximum Ratio of Similarity - Belarus Olympiad Problem
- Maxwell's Theorem [Java]
- May the Product of Planes Be a Sphere?
- Mechanical Proofs of the Pythagorean Theorem
- Median in Touching Circles [Java]
- Medians
- Medians in a Quadrilateral [Java]
- Medians in a Triangle Meet at the Center: a Second Look
- Meisters' Two Ears Theorem
- Menelaus Theorem [Java]
- Metric Relations in a Triangle
- Midline in Similar Triangles [Java]
- Midpoints and Orthogonality in Isosceles Triangles [Java]
- Midpoints from Gergonne Triangle [Java]
- Midpoints of the Lines Joining In- and Excenters [Java]
- Mikhalev's Octahedrons
- Minesweeper Theorem
- Miquel's Point [Java]
- Miquel's Point of a 4-line Via Spiral Similarity [Java]
- Miquel's Theorem for Circles [Java]
- Mirror on the Wall [Java]
- Mirror property of the altitudes [Java]
- Mirror Property of Altitudes via Pascal's Hexagram [Java]
- Mixtilinear Circles and Concurrence [Java]
- Moebius Strip [avi movie]
- Möbius' Strip [Java]
- Models and Metamathematics
- Monge via Desargues [Java]
- Monge via Desargues II [Java]
- Morley Constellation [Java]
- Morley's Miracle [Java]
- Doodling and Miracles [Java]
- Morley's Pursuit of Incidence [Java]
- Lines, Circles and Beyond [Java]
- Morley's Theorem, G. Zsolt Kiss' proof [Java]
- Morley's Theorem, R. Smyth's Proof
- Proof by H. D. Grossman
- Proof by R. J. Webster
- On Motivation and Understanding [Java]
- Bankoff's Conundrum
- B. Bollobás' proof
- Morley's Redux and More [Java]
- An Unexpected Variant
- Morley's Theorem: Proof by B. Stonebridge and B. Millar
- Morley's Theorem: Proof by H. Shutrick
- Morphing [Java]
- Müller-Lyer Illusion [Java]
- Munching on Circles
- Munching on Inscribed Angles
- More On Inscribed Angles [Java]
- My logo
- Nagel Line [Java]
- Nagel point [Java]
- Nagel Point of the Medial Triangle [Java]
- Nagel's Theorem [Java]
- Napoleon's Theorem
- Napoleon-Barlotti Theorem [Java]
- Napoleon on Hinges [Java]
- Napoleon's Relatives [Java]
- Napoleon's Theorem, a generalization
- Napoleon's Theorem by Plane Tesselation [Java]
- Napoleon's Theorem by Transformation [Java]
- Generalization of Napoleon's Theorem [Java]
- Napoleon's Propeller [Java]
- Napoleon's Theorem via Two Rotations [Java]
- Napoleon's Theorem: A third proof with complex numbers [Java]
- Necker Cube [Java]
- Neuberg Sangaku [Java]
- Newly Born Pair of Siblings to Archimedes' Twins [Java]
- Newton's Construction of Conics [Java]
- Newton's Theorem [Java]
- Nine Point Circle [Java]
- Nine Point Circle: an Elementary Proof [Java]
- No Equilateral Triangles, Please [Java]
- Nobbs' Points, Gergonne Line [Java]
- Non-Eclidean Geometries
- No-Pedal Collinearity [Java]
- Occluded Wheel Illusion [Java]
- Olof Hanner's Jigsaw Puzzle [Java]
- On the Difference of Areas
- One Sheet Hyperboloid [Java]
- Optimization Problem in Acute Angle [Java]
- Octagon in Parallelogram: Overlapping Regions [Java]
- Octagon in Parallelogram [Java]
- Optical Property of Ellipse [Java]
- Orbison illusion [Java]
- Orthocenter and Three Equal Circles [Java]
- Orthocenters
- Orthocenters of Two Triangles Sharing Circumcenter and Base [Java]
- Orthocentric System From Rectangle [Java]
- Orthodiagonal and Cyclic Quadrilaterals [Java]
- Orthogonality in Isosceles Triangles [Java]
- Orthologic Triangles in a Quadrilateral [Java]
- Orthopole [Java]
- Out of Pentagon Sangaku
- Packing shapes in a plane
- Pairs of Areas in Equilateral Triangle
- Pairs of Homologous Lines under Spiral Similarities [Java]
- Pairs of Incircles in a Quadrilateral [Java]
- Pantograph [Java]
- Paper Folding & Cutting Sangaku
- Paper Folding Geometry
- Paper strip activities [avi movies]
- Paper strip activities, two strips
- Pappus' Generalization of Euclid I.47 [Java]
- Pappus' Theorem [Java]
- Dual to Pappus'Theorem [Java]
- Parabola [Java]
- Parabolic Mirror, Illustration [Java]
- Parabolic Mirror, Theory [Java]
- Parabolic Sieve of Prime Numbers
- Paragon [Java]
- Parahexagon [Java]
- Parallel Chords [Java]
- Parallel Chords II [Java]
- Parallel Chords in Ellipse [Java]
- Parallel Chords in Crossing Circles [Java]
- Parallel Lines in a Cyclic Quadrilateral [Java]
- Parallel Lines in a Quadrilateral [Java]
- Parallelogram and Similar Triangles [Java]
- Parallelogram Illusion [Java]
- Parallelogram Iterations [Java]
- Parallelogram Law [Java]
- Parallelogram Law: A PWW [Java]
- Parallelogram Law: A Tessellation [Java]
- Partition of point sets in a plane
- Partitioning 3-Space with Circles
- Partitioning a Circle
- Pascal: Necessary and Sufficient [Java]
- Pascal in a Cyclic Quadrilateral [Java]
- Pascal Lines: Steiner and Kirkman Theorems [Java]
- Pascal Lines: Steiner and Kirkman Theorems II [Java]
- Pascal's theorem [Java]
- Peacock's Tail Sangaku
- Pedal Collinearities [Java]
- Pedal Polygons [Java]
- Pedal Triangle and Isogonal Conjugacy [Java]
- Pedoe's Theorem [Java]
- Pencils of Cubics
- Pentagon, construction of
- Pentagon in a Semicircle [Java]
- Pentagon Proportions Sangaku
- Periodic patterns in sin(N) [Java]
- Perpendicular Bisectors in an Inscriptible Quadrilateral [Java]
- Perpendicular Bisectors in an Inscriptible Quadrilateral II [Java]
- Perpendicular lines in a cyclic quadrilateral from 1975 Canadian Mathematical Olympiad
- Phantom Circle and Recaptured Symmetry
- Pivot Theorem [Java]
- Plane Filling Curves [Java]
- Plane Isometries
- Plane Isometries As Complex Functions
- Plato's Geometric Numbers: can you better Sam Loyd?
- Peaucellier Linkage [Java]
- Pick's Theorem [Java]
- Poggendorff's Illusion
- Point common to two similar rectangles [Java]
- Point in a Square
- Point on Bisector in Right Angle
- Points Generated by the Nine Points
- Polar Circle [Java]
- Poles and Polars [Java]
- Polygon in a Rectangle
- Polygons: formality and intuition [Java]
- Polygons Formed by Perpendicular Bisectors [Java]
- Pompeiu's Theorem [Java]
- Poncelet's Porism [Java]
- Poncelet's Porism in Ellipses [Java]
- Poncelet's Theorem [Java]
- Ponzo Illusion [Java]
- Ponzo Illusion II [Java]
- Possible or Impossible? [Java]
- Power of a point with respect to a circle
- Problem 4, 1975 USA Math Olympiad and the Radical Axis [Java]
- Problem 4, 1975 USA Math Olympiad and Isosceles Triangles [Java]
- Problem 4, 1975 USA Math Olympiad: Normals and Tangents [Java]
- Problem 4, 1975 USA Math Olympiad: Problem 4, 1975 USA Math Olympiad: The Final Touch [Java]
- Problem 4 from the IMO 2009
- Problem in an Equilateral Triangle [Java]
- Problem in an Equilateral Triangle II [Java]
- Problem in Three Squares [Java]
- Problem of Equal Steps [Java]
- Problem of Equal Steps II [Java]
- Problem on a Pentagonal Star
- Problem with angle bisector from 1975 Canadian Mathematical Olympiad
- Problem with equal angles from 1987 IberoAmerican Mathematical Olympiad
- Projections on Internal and External Angle Bisectors [Java]
- Projective Collinearity in a Quadrilateral [Java]
- Projective infinity
- Properties of the Circle of Similitude [Java]
- Property of 6-Parpolygon [Java]
- Property of Angle Bisectors [Java]
- Property of Angle Bisectors II [Java]
- Property of Circumscribed Quadrilaterals [Java]
- Property of Points Where In- and Excircles Touch a Triangle [Java]
- Proportions in Square
- Ptolemy's Theorem
- Puzzles on graphs.
- Pythagoras' Theorem (97 proofs)
- A Neglected Pythagorean-Like Formula
- An Extra Illustration of J. E. Bottcher's Proof of the Pythagorean Theorem [Java]
- Huygens' proof
- Pythagorean Theorem by Hinged Dissection
- Pythagorean Theorem by Hinged Dissection I
- Pythagorean Theorem by Hinged Dissection II
- Pythagorean Theorem from the Shoelace Formula
- Pythagorean Theorem via an Isosceles Triangle [Java]
- False Proofs of the Pythagorean Theorem
- Pythagoras' from Bottema's [Java]
- Pythagoras' Theorem By Sheer Shearing [Java]
- Pythagoras' Theorem By Similarity [Java]
- Pythagoras' Theorem Solely By Sliding [Java]
- Pythagorean Condition in An Isosceles Right Triangle [Java]
- Pythagorean Theorem: J. Adams' Proof by Dissection [Java]
- Pythagorean Theorem: Subtle Dangers of Visual Proof [Java]
- Pythagorean Theorem By Plane Tessellation [Java]
- Pythagorean Theorem, Generalizations of
- Pythagorean Theorem in an Orthodiagonal Quadrilateral [Java]
- Pythagorean Theorem is Equivalent to Parallel Postulate.
- Pythagorean Theorem: Versluys' Proof by Dissection [Java]
- Mechanical Proof of the Pythagorean Theorem
- "Extra-geometric" proofs of the Pythagorean Theorem
- D. Houston's proof: Is it trigonometric?
- Pythagoras' from Broken Chords
- Pythagoras' from the Star of David
- Pythagorean Theorem: An Algebraic Proof with Three Trapezoids
- A Proof of the Pythagorean Theorem with Orthocenter and Right Isosceles Triangles
- Pythagoras and Vecten Break Japan's Isolation [Java]
- Pythagorean Triples [Java]
- Quadrature: A Child's Play
- Quadrilateral from a Segment
- Quadrilateral With Equal Opposite Sides And Angles [Java]
- Quadrilateral with 3 Equal Sides [Java]
- Quadrilaterals Formed by Perpendicular Bisectors [Java]
- Quest for Paragon [Java]
- Radical Axis and Center, an Application [Java]
- Radical Axis of Circles Inscribed in a Circular Segment [Java]
- Radical Center [Java]
- Radius and Construction of a Mixtilinear Circle [Java]
- Radius of a Circle by Paper Folding [Java]
- Random Dot Stereograms [Java]
- Ratios and Orthogonality in a Triangle - Problem from the 2006 Romania MO
- Rational Points On a Circle
- Reflection In Line [Java]
- Reflections in Ellipse [Java]
- Reflections of a Line Through the Orthocenter [Java]
- Reflections of a Point on the Circumcircle [Java]
- Reflections of the Circumcenter
- Reflections of the Orthocenter [Java]
- Reflections of the Orthocenter II
- Regular Polygons in a Triangular Grid [Java]
- Regular Polyhedra - Platonic Solids
- Tetrahedron [Java]
- Octahedron [Java]
- Cube [Java]
- Icosahedron [Java]
- Dodecahedron [Java]
- Cube In Octahedron [Java]
- Octahedron In Cube [Java]
- Icosahedron In Cube [Java]
- Other Solids
- Regular Pentagon Inscribed in Circle by Paper Folding
- Regular polyhedra and Euler's Theorem
- Relations in a Cyclic Polygon
- Remarkable Line in a Quadrilateral [Java]
- Remarkable Line in Cyclic Quadrilateral [Java]
- Rendezvous [Java]
- Reverse Spoke Illusion [Java]
- Revolving Circles Illusion [Java]
- Rhombus in a Cyclic Quadrilateral [Java]
- Riemann Sphere and Möbius Transformation
- Right Triangles on Sides of a Square [Java]
- Rotating Top Illusion [Java]
- Rotating Gears [Java]
- Rotation Transform [Java]
- Product of Rotations [Java]
- Rotations in Disguise [Java]
- Rouse Ball's Fallacy [Java]
- Rusty Compass Construction of Equilateral Triangle [Java]
- Salinon: From Archimedes' Book of Lemmas [Java]
- Sam Loyd's Geometric Puzzle
- Sam Loyd's Son's Dissection [Java]
- Sangaku: Reflections and the Phenomenon
- Sangaku: Critique of My View and a Response
- Sangaku and The Egyptian Triangle
- Sangaku in a Square
- Sangaku Iterations, Is it Wasan? [Java]
- Sangaku with 8 Circles
- Sangaku with Angle between a Tangent and a Chord [Java]
- Sangaku with Quadratic Optimization
- Sangaku with Three Mixtilinear Circles [Java]
- Sangaku with Versines [Java]
- Sangakus with a Mixtilinear Circle [Java]
- Scintillating Grid Illusion [Java]
- Schwarz Lantern [Java]
- Secant Angles [Java]
- Secant Angles II [Java]
- Secant, Normal, Tangent [Java]
- Secant, Tangents and Orthogonality [Java]
- See-Saw Lemma [Java]
- Segment Trisection [Java]
- Segment Trisection Induced by Parallels to Medians [Java]
- Separating point sets with a circle
- Sequences of Touching Circles
- Serendipitous Beauty [Java]
- Serendipitous Proofs Of The Pythagorean Theorem
- Seven Circles Theorem [Java]
- Shaggy Dog Theorem
- Shapes in a lattice
- Shapes of constant width [Java]
- Shearing and Translation in Pythagorean Pants [Java]
- Shearing a Polygon into a Triangle of Equal Area [Java]
- Shearing Butterflies in Quadrilaterals [Java]
- Shepard's Parallelogram Illusion [Java]
- Shifting Cube Illusion [Java]
- Shimmer Illusion [Java]
- Short Construction of the Geometric Mean
- Shortest Fence in a Quarter-Circle Pasture
- Shredding the torus
- Sierpinski Gasket By Common Trema Removal [Java]
- Sierpinski Gasket Via Chaos Game [Java]
- Sierpinski Gasket by Trema Removal [Java]
- Similar Triangles And More
- Similar Triangles on Sides of a Quadrilateral [Java]
- Similar Triangles on Sides and Diagonals of a Quadrilateral [Java]
- Simple dissection of an acute triangle
- Simple Quadrilaterals Tessellate the Plane [Java]
- Simson Line [Java]
- Simsons and 9-Point Circles in Cyclic Quadrilateral [Java]
- Simultaneous Contrast Illusion [Java]
- Simultaneous Contrast Illusion II [Java]
- Simultaneous Contrast: Koffka's Illusion [Java]
- Simultaneous Contrast: White's Illusion [Java]
- Simultaneous Contrast: White's Illusion, V-Variant [Java]
- Simultaneous Diameters in Concurrent Circles [Java]
- Simultaneous Generalization of the Theorems of Ceva and Menelaus
- Sine and Cosine of 15 Degrees Angle
- Sine, Cosine, and Ptolemy's Theorem
- Six Circles Theorem (Bui Quang Tuan) [Java]
- Six Circles Theorem (Elkies) [Java]
- Six Circles Theorem (Evelyn) [Java]
- Six Concyclic Points [Java]
- Six Concyclic Points II [Java]
- Six Incircles in an Equilateral Triangle [Java]
- Six Point Circle [Java]
- SixPoints, ThreeLines [Java]
- Soddy Circles and David Eppstein's Centers [Java]
- Some Properties of Napoleon's Configuration [Java]
- Sperner's Lemma [Java]
- Spiral Similarity [Java]
- Square and Circle in a Gothic Cupola
- Square From Nowhere [Java]
- Square in a Circle Inscribed in a Square [Java]
- Square in a Right Triangle [Java]
- Square in Chair [Java]
- Square Inscribed in a Triangle [Java]
- Square Inscribed in a Triangle II [Java]
- Square, Similarity and Slopes [Java]
- Squares and Straight Tetrominoes
- Squares in Circles [Java]
- Squares in Semicircle and Circle
- Squares in Triangles
- Squares Inscribed In a Triangle III [Java]
- Squares on Sides of a Quadrilateral [Java]
- Square out of a Quadrilateral
- Squaring a circle
- Squaring a Rectangle [Java]
- Squinting Eyes Theorem [Java]
- SSA
- SSS
- Staircase Illusion [Java]
- Star of David [Java]
- Steiner's Sangaku
- Steiner's Theorem
- Stereographic Projection [Java]
- Stereographic Projection and Inversion
- Stereographic Projection and Radical Axes
- Stewart's theorem
- Straight Edge Only Construction of Polar
- Structural Constellation [Java]
- Sum of Squares in Equilateral Triangle
- Sum of Squares of Distances to Vertices
- Symmedians
- Symmedian and Antiparallel [Java]
- Symmedian and 2 Antiparallels [Java]
- Symmedian and the Tangents [Java]
- Symmedian in a Right Triangle [Java]
- Symmetries in a Triangle
- Tangency Point of Two Circles [Java]
- Tangent and Secant [Java]
- Tangent as a Radical Axis [Java]
- Tangent Circles and an Isosceles Triangle [Java]
- Tangent Circles in a Parallelogram [Java]
- Tangent in Concurrency [Java]
- Tangent Lines and Circles in Convex Quadrilateral [Java]
- Tangent to two circles
- Tangents and Diagonals in Cyclic Quadrilateral [Java]
- Tangents, Perpendiculars and Geometric Mean [Java]
- Tarski-Banach Decompositions
- Taylor circle [Java]
- Terquem's Theorem [Java]
- Tesseract [Java]
- The 80-80-20 Triangle
- The Chaos Game: Address Space vs IFS [Java]
- The only rational triangle
- Thébault's Problem I [Java]
- Thébault's Problem II [Java]
- Thébault's Problem III [Java]
- Thébault's Problem III, Proof [Java]
- Thébault's Problem IV [Java]
- Theorem of Complete Quadrilateral [Java]
- Theorems of Ceva and Menelaus, an Illustrated Generalization [Java]
- Three Circles and Common Tangents
- Three Circles through the Incenter
- Three Concurrent Circles [Java]
- Three Congruent Circles by Reflection [Java]
- Three Congruent Circles by Reflection II [Java]
- Three Congruent Circles by Reflection III [Java]
- Three Equal Circles in a Semicircle
- Three Incircles In a Right Triangle [Java]
- Three Incircles in a Triangle [Java]
- Three Isosceles Triangles [Java]
- Three Orthogonal Circles Through Three Given Points [Java]
- Three Parallels in a Triangle [Java]
- Three Points on a Parabola [Java]
- Three Pyramids are Better Than Two [Java]
- Three regions sharing a common boundary
- Three Similar Polygons [Java]
- Three Similar Triangles [Java]
- Three Similar Triangles II [Java]
- Three Squares and Two Ellipses [Java]
- Three Tangent Circles [Java]
- Three Tangents, Three Chords in Ellipse [Java]
- Three Tangent Circles Sangaku
- Three Tangents Theorem [Java]
- Three Tangents, Three Secants [Java]
- Three Touching Circles [Java]
- Tiling a Chessboard with Dominoes
- Toothpick Construction of a Square [Java]
- Topological preliminaries
- Torque as a Mathematical Object
- Touching Circles [Java]
- Touching Circles and Concurrency [Java]
- Touching Circles with Given Centers II [Java]
- Train wheel quandary
- Transitivity in Action [Java]
- Translated Triangles [Java]
- Translation Transform [Java]
- Triangle ABC is right iff sin²A + sin²B + sin²C = 2
- Triangle Areas in a Parallelogram [Java]
- Triangle Areas in a Parallelogram II [Java]
- Triangle Classification [Java]
- Triangle constructions and facts [Java]
- Triangle Sliding on Two Straight Lines [Java]
- Triangles, Squares and Areas from Temple Geometry [Java]
- Triangles with Equal Area [Java]
- Triangular Billiard [Java]
- Triangulating Squares
- Trigonometric Form of Ceva's Theorem [Java]
- Trigonometric Functions [Java]
- Trigonometric Identities with Arctangents
- Trigonometric Proof of the Pythagorean Theorem
- Trigonometry by Paper Folding
- Trisectable angle that is not constructible
- Tucker Circles [Java]
- Tucker Circles Through Homothety [Java]
- Twelve Matchsticks Area Puzzle
- Twisted Cord Illusion [Java]
- Two Altitudes, One Midpoint
- Two Arbelos, Two Chains
- Two Cevians and Proportions in a Triangle
- Two Circles and a Limit - Analytic Proof
- Two Circles and One More [Java]
- Two Circles and Two More [Java]
- Two Circles in a Parallelogram [Java]
- Two Circles Inscribed in a Parallelogram [Java]
- Two Circles in a Square [Java]
- Two Circles in a Square II [Java]
- Two Circles in an Angle [Java]
- Two Circles on Angle Bisector [Java]
- Two Circles on a Side of a Triangle [Java]
- Two Circumcircles And Two Pairs of Parallels [Java]
- Two Circumcircles in Triangle [Java]
- Two coins puzzle
- Two Congruent Circles by Reflection [Java]
- Two Color Coloring of the Plane [Java]
- Two Equilateral Triangles [Java]
- Two Homotheties in a Parallelogram [Java]
- Two Intersecting Circles [Java]
- Two Lines - Two Circles [Java]
- Two Parallels in a Triangle and One More [Java]
- Two Perpendiculars From a Point to a Line [Java]
- Two Planar Constructions Related to a 3D Problem
- Two Quadrilaterals [Java]
- Two Quadruplets of Tangent Circles [Java]
- Two Sangaku with Equal Incircles
- Two Simsons in a Triangle [Java]
- Two Squares and Another Square [Java]
- Two Symmetric Triangles Are Directly Decomposable [Java]
- Two Touching Circles [Java]
- Two Triangles With Common Base and Altitude [Java]
- Two Triples of Concurrent Circles [Java]
- Two Triples of Similar Triangles [Java]
- Unfolding Spirals Illusion [Java]
- Urquhart's Theorem
- USA 1975 Problem 4
- Use of Homogeneous Coordinates for Geometrical Calculations
- Van Obel Theorem, Determinants, and Barycentric Coordinates
- Van Schooten's and Pompeiu's Theorems [Java]
- Van Schooten's Locus Problem [Java]
- Variations on the Theme of Tremas [Java]
- Variations on the Theme of Tremas II [Java]
- Varignon Parallelogram [Java]
- Various Geometries
- Vecten's Collinearity [Java]
- Vecten's Mesh [Java]
- Vector Addition and Subtraction [Flash]
- Vector product
- Versatile Theorem [Java]
- Viewing a Statue
- Viviani's Theorem [Java]
- Viviani's Theorem II [Java]
- Viviani in Isosceles Triangle [Java]
- Viviani by Inversion
- Viviani by Vectors
- Volumes of Two Pyramids
- Wallace-Bolyai-Gerwien Theorem
- Wallace's Theorem [Java]
- Watt's and Chebyshev's Linkage [Java]
- Weird curves bound normal areas
- Weitzenböck Inequality [Java]
- What does one see inside a spherical mirror? [Java]
- What Is Analytic Geometry?
- What Is Angle?
- What Is Area?
- What Is Ellipse?
- What Is Line?
- What Is Point?
- When a Triangle is Equilateral [Java]
- When index equals content [Java]
- Why a Diameter Is the Longest Chord?
- William Wallace's Proof of the Butterfly Theorem
- Wittenbauer's Parallelogram [Java]
- Wundt Illusion [Java]
- Wundt Block Illusion [Java]
- Y. Sawayama's Lemma [Java]
- Y. Sawayama's Theorem
- Zaslavsky's theorem [Java]
- Zöllner's Illusion [Java]
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