Abacus in Various Number Systems
Abelian group
Abscissa
Absolute Geometry
Absolute value
Absolute value of a complex number
Absorbtion identity
Abundant Number
Acute angle
Acute triangle
Adams' Circle
Adams' Method of Apportionment
Addition
Addition Formula for Sine
Additive Inverse
Additivity
Adjacency
Affine-regular Polygon
Affine Geometry
Affine Space
Affine Transformation
Affirmative Action Problem
Alabama Paradox
Alexander the Great
Algebraic numbers
Algorithm
Aliquot part
All Triangles Are Isosceles
Alternate Angle
Alternating group
Altitude
An Airline Problem
Anallagmatic
Analog gadgets
Angle
Angle Bisectors
Angle of incidence
Angle of reflection
Angle preservation property
Angle Trisection
Angular distance
Annulus
An Old Japanese Theorem
Anticenter of a Quadrilateral
Antichain
Antichain in lexicographic order
Anticommutativity
- Anticommutative quasigroup
Anticomplementary Triangle
- Anticomplementary Triangle
Antiequilic Quadrilateral
Antihomologous
Antiparallel
- Antiparallel
Antipedal triangle
Antisymmetry
Apollonian Gasket
Apollonian Circles
Apollonian Circles Theorem
- Apollonian Circles Theorem
Apollonian Family of Circles
Apollonius Problem
Apollonius' Theorem
Apportionment Problem
Arbelos
Arc (in circle)
Archimedes' Law of the Lever
Archimedes of Syracuse
Archimedes Triangle
Archimedes' Lemma
Archimedes' Method
Archimedes' spiral
Archimedes' Squaring of Parabola
Archimedes' Twin Circles
Area of a Parallelogram
Area of a Ring
Areal Coordinates
Argand Diagram
Argument of a Complex Number
Arithmetic mean
- Arithmetic-Geometric Mean Inequality
Arithmetic Operations in Various Bases
Arithmetic Paradoxes
Arithmetic Series
Articulation (node) of a graph
ASA
Assimilation Illusion
Associativity
- Associativity
Associates
Astroid
- Astroid
Asymmetric Propeller
- Napoleon's Propeller
Asymmetry
Attractive Point
Automaton
Automorphism
Axiom of Choice
Axiom schema
Axiomatic Completeness
Axis of Homothety
Axis of Symmetry of a Conic

Bachet's Magic Trick
A Baffling Prediction
Balinski and Young's Impossibility Theorem
Banach-Tarski Decomposition
Bankoff's Conundrum
Banzhaf Index
Barbier's Theorem
- Barbier, The Theorem of
Barcode Encoding
Barycenter, barycentric coordinates
- 3 Jugs Problem
- 3 Glasses Problem in Barycentric Coordinates
- Barycentric coordinates and Geometric Probability
Base Converter
- Algorithms for Base Conversion
- Conversion of Fractions in Various Bases
Basic Rigid Motions of the Plane
Basil Rennie's Lemma
Bayes' Theorem
Bear cubs problem
Beatty Sequences
Beecroft's Theorem
Benford's Law
Benham's Top
Bernoulli Trials
Bernstein theorem
Bertrand's Paradox
Bevan's Point and Theorem
BÃ©zout's Identity
BÃ©zout's Lemma
Bicentric Quadrilateral
Bicolor Towers of Hanoi
Bijection
Bilateral Diagram
Bimedians (in a tetrahedron)
Binary Encoding with the Stern-Brocot tree
Binary Euclid's Algorithm
Binary Relation
Binary System
Binet's Formula
Binomial Coefficient
Binomial Distribution
Binomial Theorem
Bipartite graph
The Birthday Problem
Bisectal Circle
Bisecting arcs
Bisecting a shape
Bitwise shift
Bitwise boolean operations
Blithe 12 puzzle
Blivet
Block Design
Bogus Nim
- Bogus Nim
Bolzano Theorem
- Bolzano Theorem, proof
Bookland
Bottema's theorem
Bound
Bound Variable
Boundary point
Bounded Distance
Brahmagupta's Theorem
Brahmagupta's formula
Braids Theory
Braikenridge-Maclaurin Theorem
Breaking Chocolate Bars
Brianchon's theorem
Brick Wall Illusion
Bride's Chair
Brocard angle
Brocard circle
Brocard diameter
Brocard points
Broken Chord Theorem
Brouwer's Fixed Point Theorem
Buffonï¿½s Needle Problem
- Math Surprises
Bulging lines illusion
Butterfly Theorem
- A Better Butterfly Theorem
- Two Butterflies Theorem
- The Lepidoptera of the Circles
Byzantine Basketball

Cabart's Collinearity
Cake cutting
Calendar Magic
Calisson
Candy's Theorem
Canonical Equation of Conics
Canter
Cantor Function
Cantor set
- Cantor set of positive measure
- C0 - C0 = [-1, 1]
Cantor's lines
Cantor's point
Cantor's theorem
Cantor-Bernstein-Schroeder theorem
Cardinal
- Cardinal Numbers
Cardioid
- Hearty Munching on Cardioids
Carnot's Theorem
Carnot's Theorem
Carnot's Theorem (Generalization of Wallace's Theorem on simsons)
Carpets Theorem
Cartesian coordinates
- Cartesian coordinate system
Cassini's identity
Cauchy's inequality
Cauchy's limit
Cauchy sequence
Cavalieri's Principle
Cayley's Lines
Cayley Table
Cayley's Theorem
Ceiling Function
Cellular Automaton
Center Circles
Center of Inversion
Centipede
Central Angle
Central Similarity
Central Limit Theorem
Centroid
- Centroid, a Characteristic Property Of
Circle of Similitude (of three directly similar figures)
Circle of Similitude (of two circles)
Ceva's Theorem
- Ceva's Theorem and Fibonacci Bamboozlement
- The Menelaus theorem
- Trigonometric Form of Ceva's Theorem
- Ceva is equivalent to Menelaus I
- Ceva is equivalent to Menelaus II
Cevian
Cevian Nest
Cevian Triangle
- Cevian Triangle
Changing Colors
Chaos
Characteristic Constants of the n-Line
Characteristic function
Chasles' Theorem
Chebyshev polynomials
Checker - jumping
Chevalier de Mï¿½rï¿½'s Problem
Chinese Remainder Theorem
Chord (in circle)
Chronology of updates
Chvatal's Art Gallery Theorem
Circle
Circle of Apollonius
Circle of Concern
Circle of Influence
Circle-Stacking Theorem
Circuit, same as cycle
Circulant Matrix
- Circulant Matrix: example
Circular Coordinates
Circular Poggendorff Illusion
Circumference
Circum-orthic Triangle
Circumcenter
- Existence of 1
Circumcevian Triangle
Circumcircle
Circumpedal Triangle
Circumradius
Circumscriptible Polygon
City-block distance
Classification of Triangles
Cleavance center
Cleaver
Clifford's Chain
Clifford's Lemma
Clinant
Closed interval
Closed set
Closed walk
Closure
Coalition
Coaxal circles
Coaxal Circles Theorem
Coincidence
Collatz Conjecture
Collinear points
Collage Theorem
Column vector
Combination
Combinatorial Proofs
Common Fraction
Common Notions of Euclid
Commutative group
Commutativity
Compact sets
Compactification
Comparing complex numbers.
Complementary angles
Complementary event
Complementary sequences
Complete graph
- Complete graph
Complete order
Complete Quadrangle
Complete Quadrilateral
- Complete Quadrilateral, the Theorem of
- Diagonals of the complete quadrilateral
Completeness
Completion of a Space
Completing the Square and Quadratic Formula
Complex numbers
Complex product of Complex Numbers
Complex Projective Line
Composite number
Composition
Compound Interest
Concatenation
Concentric circles
Concentric polygons
Concurrent lines
Concyclic Points
Conditional Probability
Cone
Conformal
Congruent sets
Congruence Modulo a Number
Conic Sections
Conjugate complex numbers
Conjugate coordinates
Conjugate Diameters in Ellipse
Conjugate families of circles
Conjugate points
Conjunction
Connected component of a graph
Connected graph
Connected set
Consecutive Isosceles Decomposition
Consistency
Constant Chord
Constant Random Variable
Constant width, shapes of
Constructible Numbers
Construction problem
Construction with the Compass Only
- Rusty Compass Construction of Equilateral Triangle
Contact Triangle
Content
Continuity
Continued fraction
- Continued Fractions on the Stern-Brocot Tree
Continuous Line Illusion
Continuum
Continuum Hypothesis
Contraction Mapping Theorem
Convergent
Convergent Sequence
Convergent Series
Converse theorem
Convex hull
Convex shape
Convolution
- Convolution
Conway's Circle
Coolidge theorem
Coordinate
Copernicus' Theorem
- Proof of Copernicus' Theorem
Coprime
Cosine Rule
- Another derivation
- In a vector space
Countable sets
Counting: The Beginning of Mathematics
- Let Them Count
Counting numbers
Covering A Chessboard With Domino
Critical Player
Cross product
Crosscap
Crossing Diagonal Method
Crossing Number of a Graph
Crossover
Cross-Ratio
Crossed-Lines Construction of Shapes of Constant Width
Curve
CTK Exchange, the
Curry's Paradox
Curvilinear triangle
Cutting pipes
Cycle (a permutation)
Cycle (on a graph), same as circuit
Cyclic quadrilaterals
- Brahmagupta's Theorem
- Four Concurrent Lines in a Cyclic Quadrilateral
- Incenters in Cyclic Quadrilateral
- Remarkable Line in Cyclic Quadrilateral
Cycloids
Cyclotomic Equation
Cylinder

Dart
Data Structure
Date Game
Day's Sine Illusion
de Bruijn cycle
Decimal numeral
Decomposition by Dissection
Defect of a Langford Sequence
Deficient Number
Degree of a vertex
Delboeuf Illusion
Delian Problem
- Delian Problem Solved
Deliberate Ambiguities
Deltahedron
Deltoid
- Steiner's Curve
de Moivre's formula
- de Moivre's formula
De Moivre numbers
de Morgan's Formulas
Demagoguery
Denuminator
Dependent Events
Dense set
Density function
Density (of a binary relation)
Derangement
Desargues' Theorem
Descartes' formula
Descartes' Rule of Signs
Devilï¿½s pitchfork
Diagonal Count
Diagonal matrix
Diagonal process
Diagonal Triangulation
Diagonals of the complete quadrilateral
Diameter of a circle
Diameter of a triangulation
Diameter of a convex shape
Dihedral Symmetry
Difference of two sets
Digital Root
Digits, fun with
Digraph
Dilation
Dimensional Analysis
Direct product
Direct sum
Directed Angle
Directly Congruent Figures
Directly Equidecomposable
Directrix
- Directrix of an Ellipse
Disappearing Lines (puzzle)
Disconnected graph
Discovery of Duane DeTemple
Discriminant of Quadratic Expression
- Discriminant of Quadratic Equation
  - Disjoint Events
  - Disjunction
  - Disjunctive Rule
  - Disjunctive sum of games
  - Distance
  - Distance Between Strings
  - Distance Formula
  - Distance From a Point to a Straight Line
  - Distance on the sphere
  - Distance to the Horizon
  - Distorted Lines Illusion
  - Distributive Laws
  - Divergent Series
  - Divide a segment into n equal parts
  - Divisibility by 3
  - Divisibility by 7
  - Divisibility by 9
  - Divisibility by 11
  - Divisibility by 81
  - Divisibility Criteria
  - Divisor of zero
  - d'Ocagne's identity
  - Dodecagon
  - Dot Patterns and Sierpinski Gasket
  - Do you know that...
  - Dot product
  - Double Factorial
  - Double Generation Theorem
  - Double negative
  - Double angle formula for sine
  - Doubling the Cube
  - Douglas' Theorem
  - Drawing circles and ellipses
  - Droodles
  - Droz-Farny Circles
  - Droz-Farny Line Theorem
  - Dual to Pappus' Theorem
  - Duality
  - Duality Principle
  - Ducci Sequence
    - Ducci Sequence
  - Duplication of the Cube
  - Dumb Parrot
  - Dynamic Construction of Ellipse and Other Curves

8-connectedness
EAN-13 encoding
Ear
Eccentricity
Edge
Egyptian Multiplication
Egyptian Triangle
- Egyptian Triangle By Paper Folding
Eigenvalue
Eigenvector
- Eigenvectors by Inspection
Eliminand
Empty set
Exterior Angles formed by a secant and parallel lines
Epicycloids
Eppstein's points
Equation
Equation of a Straight Line Through Two Points
Equation of a Straight Line with Two Intercepts
Equal Incircles Theorem
Equality
Equiangular polygon
- A Property of Equiangular Polygons
Equichordal points: Just Do It
Equidecomposable shapes
Equilateral polygon
Equilateral triangle
Equilic Quadrilateral
Equivalence Relations
The ErdÃ¶s-Mordell Inequality
Euclid's Algorithm
- Almost Integers, Euclid's Algorithm
- Extension of Euclid's Algorithm
Euclid's Game
Euclid's proof of the Pythagoras' Theorem
Euclidean distance
Euler Line
Euler-Nagel Line
Euler's Characteristic
Euler's Formula
- Euler's Formula
Euler's FormulaEuler's Formula and Poncelet Porism
Euler's Function and Congruence Theorem
Euler-Mascheroni Constant
Euler points
Euler's Theorem
Euler's Points
Euler's Triangle
Euler walk
Even permutation
Even vertex
Evolution of Algebraic Symbolism
Excenter
Excentral triangle
Excircle
Existential Import
Existential Quantifier
Exscriptible Quadrilateral
Extended Argument of a Complex Number
Extension Fields
Extension of Euclid's Algorithm
Exterior Angle Theorem - an appreciation
External Bisector
- External Angle Bisector
External product
External Symmedian
External Tangent to Two Circles
"Extra-geometric" proofs of the Pythagorean Theorem
Extreme
Extreme points of convex figures
Extreme Value Theorem
Eyeball Theorem
Eye Opener Series

4-connectedness
4 Knights
4 travellers problem
4x4 coloring problem
Factorial
Factorials and division
Factoring polynomials
Fagnano's problem
- Fagnano's Problem, Third Solution
- Fagnano's Problem in Reverse
- L. Fejer's Solution
Fair Division
- Method fo Lone Divider
- Method of Markers
- Method of Sealed Bids
Fallacy
Farey Series
Feasible vectors
Fechner Colors
Fermat's Little Theorem
Fermat Numbers
Fermat Point and Generalizations
- Fermat-Torricelli Point
- Fermat's Point
Feuerbach's Point
Feuerbach's Theorem
Fibonacci sequence
- Ceva's Theorem and Fibonacci Bamboozlement
- Fibonacci Nim
- Fibonacci Numbers
Field
Fifteen, the puzzle of
Fifth Postulate
Finite Cover Property
Finite Intersection Property
- Infinity in Compactification
Finsler-Hadwiger theorem
First Napoleon Point
First Theorem of Apollonius
Fish Soup Game
Five Incircles Theorem
Fixed point
- About a Line and a Triangle
Flank (triangle)
Flipping pancakes
Floor
Focal Chord
Focal Distance
Focal Parameter
Focal Radius
Focus of a Conic
- Foci of an Ellipse
Folding
Ford's touching circles
Formal Framework
Four 3s
Four 4s
Four 5s
Four Geometric Problems of Antiquity
Fourth Proportional
Fractal
Fraction Game
Fractional part
Free group
Free Variable
Friendly Kiepert's Perspectors
Friendship
Friendship Theorem
Frieze Patterns
Frogs and Toads
Frogs and Toads in 2 dimensions
Fulcrum
Full angle
Function
Function spaces
Functional equation
Fundamental Theorem of 3-Bar Motion
Fundamental Theorem of Algebra
Fundamental Theorem of Arithmetic
- Almost Integers, Fundamental Theorem of Arithmetic
Fundamental Theorem of Directly Similar Figures
Funny Arithmetic
Fuss' Theorem

Galois Extensions
Game of Hex
Game Theory
Gauss-Bodenmiller theorem
Gaussian coordinates
Gaussian Integers
Gelfond's theorem, Gelgond-Schneider theorem
General Equation of a Straight Line
General position, lines in
Generalization in Mathematics
Generating Function
Genetic Algorithms
Geoboard, Toying with the
Geometric Constructions
Geometric mean
- Arithmetic-Geometric Mean Inequality
Geometric series
- Sum of the geometric series
Gerbino's Illusion
Gergonne and Van Obel Theorems
Gergonne Line
Gergonne Point
Gergonne Triangle
Gergonne's Magic Trick
Gibbs, Josiah Willard
Gion Shrine Problem
Girth of a Graph
GLaD Construction
Glide Reflection
Glider
Gnomon
GÃ¶del's Incompleteness Theorem
Golden rectangle
Golden section
- Golden Ratio in Geometry
Golden triangle
Googol
Gordius, King of Phrygia
Gradient
Graph
Graph Theory
Gray codes
Greatest Common Divisor (gcd)
Grebe's theorem
Greedy algorithm
Griffiths' theorem
Group
Groupoid
Growth
Grundy number
Grundy's Game
Guest book

Hadwiger-Finsler Inequality
Half-axis
Half-turn
Hamilton Cycle
Hamilton Path
Hamilton's Method of Apportionment
Hamilton's theorem
Hamming Distance
Handshake Lemma
Hanoi, Tower of
Happy 8 puzzle
Harmonic bundle
Harmonic conjugates
Harmonic Mean
- Harmonic mean
Harmonic Ratio
Harmonic Series
Harmonic Triangle
Hart Circle
Hart's Inversor
Hart's Theorem
Haruki's Lemma
Haruki's Theorem
Hausdorff Distance
Heaviside Step Function
Height in a triangle, formula for
Hering Illusion
Heptadecagon
Heptagon
Heredity
Hering Illusion
Hermann Grid Illusion
Heron's Formula
- Derivation
Heron's Problem
Hex Can't End in a Draw
Hex numbers
Hilbert's Plane Filling Curve
Hjelmslev Theorem
Hofstadter Triangles and Points
Hole
Homogeneous Coordinates
Homogeneous Functions
Homologous
Homothety
- Homothety
Hooked Langford Sequence
Hooper's Paradox
Hopf Fibration
Horner's Method
Hour glass timing
How to define a permutation?
Human calculators
Hummer's Mind Reader
Huntington-Hill's Method of Apportionment
Huzita's axioms of paper folding
Hyperbinary expansion
Hypercube
Hyperintegers and Hyperreal Numbers
Hypocycloids

Ian McGee's Observation
Ideal elements
Ideal subrings
Idempotent law
Identical Twins Puzzle
Identical Transformation
Identity
Identity matrix
iff
Illusory contour
Imaginary numbers
Imaginary Part of a Complex Number
Impartial gameA second look
Implication
Implicit Equation of a Straight Line
Impossible Fork
Impossible page
Improper Isometry
Incidence matrix
Incident points and lines
Incenter
Incenters in Cyclic Quadrilateral
Incircle
Inclusion-Exclusion Principle
- Marriage Theorem
Incompatible Events
Indegree
Independent Events
Index
Index Lemma, the
InductionMathematical Induction: examples
Infinite Discent for x4 + y4 = z4
Infinite Products
- Convergent
- Divergent
- Convergent to 0
- Divergent to 0
Infinite Sums
Infinitesimal
Infinitude of Primes
Infinity
- Infinity and Probability
- What Is Infinity?
Inflectin point
Injective function
Inner product
Inner Soddy circle
Inradius
Inscribed Angles
Inscriptable (inscriptible) Polygons
Integer
Integer Iterations on a Circle
Integral Domain
Integration in Spherical Coordinates
Intercept
Intercepted Arc
Interest Calculations
Interior Angles formed by a secant and parallel lines
Intermediate Value Theorem
Internal point
Internal Tangent to Two Circles
Internet News sites
Intersecting Chords (Secants) Theorem
- Intersecting Chords Theorem
Intersection of sets
Intouch Triangle
Invariant Set
Inventor's Paradox
Inverse Element
Inversion (combinatorial)
Inversion (geometric)
- Inverse image
- Inversion
- Inversion Tool
- Inversion with Negative Power
Invert the Divisor and Multiply
Involution
Irrational numbers
ISBN Encoding
Isogonal lines
- Isogonal circle
- Isogonal conjugates
- Isogonal Conjugality
- Isogonal Concurrency
Isogonic Centers
Isolated point
Isometry
- Plane Isometries
Isosceles trapezoid
Isosceles Tetrahedron
Isosceles triangle
Isotomic lines
Isotomic conjugates
Isoperimetric Inequality
Isoperimetric Theorem
Isoperimetric Theorem, a variation on
Isoperimetric Theorem, a different one
Iterative process

Jam
Japanese Theorem I
Japanese Theorem II
Jefferson's Method of Apportionment
Joachimsthal's Notations
John Sharp's Paradox
Johnson-Trotter Method
Jordan Curve Theorem
Josephus Flavius, a legend and a problem
Judd Illusion
Julia sets
Jump

Kanizsa Triangle
Kantor's Circle
Kaprekar's constant
Kaprekar's process
Kayles
- Grundy function for Kayles
Kiepert's Theorem
Kiepert's Perspector
Kirkman's Theorem
- Pascal Lines: Steiner and Kirkman Theorems II
Kitaoka's waves
Kite
Klein Bottle
Knots
Koch's snowflake
Koffka's Illusion
KÃ¶nigsberg
KÃ¶nigsberg Bridges
Kronecker's symbol
Kruskal's algorithm
Kurschak's Tile and Theorem

La Hire's Theorem
- La Hire's Theorem, a Variant
- Joachimsthal's Notations
Labeling of a graph
Lagrange's identity
- Lagrange's identity, Proof
Lagrange's polynomial
Lambert's Theorem
Langford Sequence
Langman's Paradox
Latin Squares
Lattice
Lattice
Lattice Multiplication
Latus Rectum
Law of Cosines
Law of excluded middle
Law of Sines
La Hire's Theorem
Leaf
Leap Year
Least Common Multiple (lcm)
- Algorithm for Computing LCM
Left-handedness
Leibniz Triangle
Legendre's Lemma
Lemoine antiparallel
Lemoine circles
Lemoine hexagon
Lemoine line
Lemoine point
LÃ©on Anne's theorem
Leonardo's Claws
The Lepidoptera of the Circles
The Lepidoptera of the Quadrilateral
Level Curve
Levenshtein Distance
Lewis Carroll's problem
Lewis Carroll's Game of Logic
Lexicographic order
- Complex numbers
- Permutations
- Pigeonhole
Lights Out
Lindemann's Theorem
Line at infinity
- Line at Infinity
- Line at infinity
Linear combination
Linear function
Linear order
Linear Programming
Linear Space
Linear Transformation
Lines in general position
Liouville's Theorem
Listing all permutations
Local-Global Principle
Locus
Logarithmic spiral
Logistic equation
Logistic model
Logo of mine
Lone Divider Method
Long Multiplication
Long Runs of Composite Numbers
Looking your best
Loop
Looping Chips
Lowest Terms, fraction in
Loyd's Puzzles, Sam
- Can you better Sam Loyd?
- Farmer and Wife To Catch Rooster and Hen
- Sam Loyd's fifteen
- Sam Loyd's Geometric Puzzle
- Plato's Geometric Numbers: can you better Sam Loyd?
- Puzzlist vs. Mathematician: A Practical Arithmetic Problem
- The Gordian Knot
Lubell-Yamamoto-Meshalkin inequality
Lucas' Theorem
- Lucas' Theorem
Lucky 7 puzzle.
Lune
LYM inequality

Maclaurin series
MacLaurin's Construction of Conics
Magic in Square
Magic Squares game
Mahavira's theorem
Major circle of ellipse
Malfatti's Problem
Maltitude
Mandelbrot and Julia sets
- Iterations and the Mandelbrot Set
Mannheim's Theorem
Manifesto
Markers Method of Fair Division
Marriage Theorem
Mascheroni constructions
MasterMind, Invitation to
Material Point
Mathematical Expectation
Matrix
A Matter of Age
Maximal Chain
Maximum Modulus Theorem
Maxwell's Theorem
Mazes
- Mazes
Mean Proportional
Mean Value Theorem
- Rolle's and Mean Value Theorems
Mechanical Proof of the Pythagorean Theorem
Medial triangle
Median triangle
Median
Median Point
Medians in a Quadrilateral
Mediant fraction
- Mediant fraction
- Dots and Fractions
Mendelsohn triple
Menelaus Theorem
- Menelaus is equivalent to Ceva I
- Menelaus is equivalent to Ceva II
Merlin's Magic Squares
Metamathematics
Metric Completeness
Metric Function
Metric Space
Mex rule
- Mex rule
Midline (in a triangle)
Millipede
Mini Lights Out
Minimal Lattice
Minimal-change Property
Minimax Principle
Minimax Theorem
Minimum element in a poset
Minimum Spanning Tree
- Minimum Spanning Tree
Minkowski addition
Minkowski subtraction
Miquel's Point
- Miquel's Point of a 4-line
- Miquel's Point of a 4-line Via Spiral Similarity
Mirror property of the orthic triangle
Mirror property of the altitudes
Mixed Product of Three Vectors
Mixtilinear Circles and Concurrence
- Radius and Construction of a Mixtilinear Circle
Mobile Integer
Model
Modulo Arithmetic
- Modular Arithmetic
Modulus of a complex number
Modus ponens
Modus tollens
MÃ¶bius Strip
MÃ¶bius Transformations
- MÃ¶bius Transformations
Mohr-Mascheroni construction
Monge Point
Monge's Circle Theorem
- Monge via Desargues
- Monge via Desargues II
Monic polynomial
Monomino
Monotone Convergence Theorem
Monty Hall Dilemma
Moore's Plane Filling Curve
Morley's Miracle
- Doodling and Miracles
Most likely number of successes in Bernoulli trials
MÃ¼ller-Lyer Illusion
Most elementary theorem of Euclidean geometry
Multiplicand
Multiplication
Multiplicative Inverse
Multiset
Mutation
Mutually Exclusive Events
Mutually prime integers
My logo

9-Point Center
9-Point Circle
- 9-point Circle as a Locus of Concurrency
Nagel Line
Nagel Point
- Nagel Point
Nagel's Theorem
Napier Bones
Napoleon Points
Napoleon's Theorem
- Napoleon's Theorem, a generalization
- Napoleon's Theorem by Plane Tesselation
- Napoleon's Theorem, two proofs
- Napoleon's Theorem, complex variables
- Napoleon's Theorem, circle incidence
- Napoleon's Propeller
Near
Necker Cube
Negative Powers
Neighborhood
Nephroid
Nested Radicals
Neuberg's Theorem
- Neuberg's Theorem, Synthetic proof
Neusis Constructions
- Neusis
New-States Paradox
Newton-Gauss line
Newton's line
Newton's Theorem
Nim, the game of
Nimble
Nimber
Nim-heap
Nim-sum
Nine-point Circle
Nine dots problem
n-Line
- Characteristic Constants of the n-Line
Nobbs' points
Non-degenerate conic
Non-Eclidean Geometries
Nonseparable Graph
Norm (of a vector)
Normal play
Normal topological space
Northcott's game
Nothing is something
Nowhere dense set
N-position
Number Line
Number Mosaics
Number System With Base 36
Numbers, types of
- Numbers, Conway's definition
Numeral
Numerator

1-1 correspondence
Obtuse angle
- Obtuse angle
Obtuse triangle
Odd permutation
Odd vertex
Oddball Problem
Old Japanese Theorem
Olof Hanner's Jigsaw Puzzle
One Pile
One-sided surfaces
Open interval
Open sets
Open walk
Operations on Fractions
Operator
Oppositely Congruent Figures
Optical Illusion
Optical Property of Ellipse
Orbison Illusion
Orbits
Order, Ordered Space
Ordinary Generating Function
Ordinate
Orientation
Origami
Orthic Axis
Orthic triangle
- Mirror property of the orthic triangle
Orthocenter
Orthocentric system
Orthodiagonal Quadrilateral
- Orthodiagonal Quadrilateral
Orthogonal latin squares
Orthogonality
Orthologic Triangles
Orthopole
Other math sites
Outdegree
Outer Soddy circle

p-adic Expansions
p-adic Numbers
Pace
Packing shapes in a plane
Palindromic
Paper Folding
Paper strip activities
Pappus' Generalization of Euclid I.47
Pappus' Theorem
- Dual to Pappus' Theorem
Parabola
- Parabola as locus
- Parabolic Mirror
- Parabola as Envelope
Paradox
Paradox of Tristram Shandy
Parahexagon
Parallel Lines
Parallel Postulate
Parallelogram
Parallelogram Law
- Parallelogram law
Parallelogram rule
Parametric Equation of a Straight Line
Parity
- Parity of a node on a graph
Parpolygon
Parrondo Paradox
Partial order
- Partial order in a lattice
Partition of point sets in a plane
Partitioning a Circle
Partizan gameA second look
Pascal's Identity
Pascal's linePascal Lines: Steiner and Kirkman Theorems
Pascal's theorem
- Pascal's theorem
- Pascal's Theorem, Homogeneous Coordinates
- Pascal in a Cyclic Quadrilateral
- Pascal in Ellipse
Pascal Triangle and Sierpinski Gasket
- Pascal Triangle and the Tower of Hanoi
Peano axioms
Peano Curves
Peano and Wunderlich's Plane Filling Curves
Peasant Multiplication
Peaucellier Linkage
Pedal circle
Pedal curve
Pedal point
Pedal triangle
Pedal Construction of Parabola
Pedal Curve
Pedoe's Theorem
Peg Solitaire
- Peg Solitaire and Group Theory
Pencil of circles
Pencil of lines
- Munching on Inscribed Angles
Penosculant
Pentagon, construction of
Percent
Perfect Langford Sequence
Perfect number
Perimeter Splitter
Periodic cycle
Periodic patterns in sin(N)
Permutation
- How to define a permutation
- Listing all permutations
- What, how, and the Web
Perpendicular bisector
Perspective triangles
- Triangles perspective from a point
- Triangles perspective from a line
Petersen Graph
p
- Determination of p
Pick's Theorem
Pigeonhole principle
- Pigeonhole Principle and Extensions
Pitot's Theorem
Pivot Theorem
Pivotal Player
Place Value
Plainim
Plainim MisÃ¨re
Planar graph
Planar polygon
Plane Filling Curves
Plato's Geometric Numbers: can you better Sam Loyd?
Plane Isometry
PlÃ¼cker's Lines
Plus or Minus
Poggendorff Illusion
Poggendorff Illusion II
- Circular Poggendorff Illusion
Point
Point at infinity
- Point at Infinity
- Point at Infinity
- Point at infinity
Point Circle
Point in a Square
Point inside a triangle
Point-Slope Equation of a Straight Line
Polar Circle
Polar coordinates
Polar Equation of conics
Pole and Polar with respect to an angle
Pole and Polar with respect to a circle
Pole and Polar with respect to a triangle
Pole
Poles and Polars
Polygon
Polygonal number
Polyomino
Pompeiu's Triangle and Theorem
Poncelet's Porism
Poncelet's Theorem
Ponzo Illusion
Ponzo Illusion II
Population Paradox
Porism
Poset
Positional Number System
Positive (Counterclockwise) Direction
Power of a point with respect to a circle
- Power of a point with respect to a circle
Power of Inversion
P-position
Predicate
Prim's algorithm
Prime
Prime Number Decomposition
Primorial
Principal
Principle of Conservation of Angular Momentum
Principle of Duality
Principle of Proportionality
Prisoner's Dilemma
Probability
- Probability density function
- Probability distribution function
Probability paradoxes
Product of Rotations
Sequential Rule
Proizvolov's Identity
Projection
Projective Geometry
Projective Plane
Pronk
Proofs Without Words
- Proof
Proper Isometry
Property of an
Propositional Variable
Protractor Postulate
Ptolemy's Inequality
Ptolemy's Theorem
- Ptolemy's Second Theorem
- Ptolemy's Theorem implies Pythagoras' Theorem
- Sine, Cosine, and Ptolemy's Theorem
- Euler's Generalization of Ptolemy's Theorem
Pure existence proof
Purely Imaginary Complex Numbers
puz(G), the graph of a puzzle
Puzzles on graphs
Pythagoras' Theorem
- Mechanical Proof of the Pythagorean Theorem
- "Extra-geometric" proofs of the Pythagorean Theorem
- Pythagorean Theorem, Generalizations of
Pythagorean triples
- Proof of the formula
- Norm of Gaussian integers
- Gaussian integers
- Divisibilty in Pythagorean Triples
- Trinary Tree(s) underlying Primitive Pythagorean Triples
Q
- Quadratic Average
- Quadratic Field
- Quadratic Formula
  - Completing a Square and Quadratic Formula
- Quadratic Function
- Quadrangle
- Quadrilateral
- Quarter-turn
- Quasigroup
  - Quasigroups and block designs from triangular grid
- Quota Rule
- Math Quotations, a Web poll

Rabinowitz's Point
Radical axis of two circles
Radical center of three circles
Radius of Inversion
Radius-vector
Radix
Ramsey Number
Ramsey Theorem
- Ramsey's Theorem is Sharp
Random Dot Stereograms
Random Event
Random Number Generator
Random Variable
Rational approximation
Rational integers
Rational numbers
Rational Root Theorem
Ray
Real numbers
Real Part of a Complex Number
Real Product of two Complex Numbers
- Real Product of Complex Numbers
Rectangle
Recurrence relations
Reflection
Reflection in Line
Reflection in Point
Reflection Law in Ellipse
Reflective Properties of Parabola
Reflex angle
Reflexivity
- Reflexivity
Regular polygon
Regular polyhedron
Relatively prime integers
Removable singularity
Repelling point
Rep-tile
Residue classes
Retinend
Reuleaux's triangle
Reverse Solitaire
Reversible move
Revolving Circles Illusion
Rhombus
Riemann Sphere
Right angle
Right triangle
Right-handedness
Rigid motions
- Rigid motion
Ring
Rolle's Theorem, the
- Rolle's and Mean Value Theorems
Rotocenter
Rottary gallop
Rounding numbers
Rouse Ball's Fallacy
Routh's Theorem
Row vector
Russell's Paradox
Russian Peasant Multiplication
Rusty Compass Construction of Equilateral Triangle

7 Coins Puzzle
Sam Loyd's Puzzles
- Can you better Sam Loyd?
- Farmer and Wife To Catch Rooster and Hen
- Sam Loyd's fifteen
- Sam Loyd's Geometric Puzzle
- Plato's Geometric Numbers: can you better Sam Loyd?
- Puzzlist vs. Mathematician: A Practical Arithmetic Problem
- The Gordian Knot
Saddle Point
Salinon: From Archimedes' Book of Lemmas
Salmon's points
Sam Loyd's fifteen
Sam Loyd's Geometric Puzzle
Sam Loyd's Son's Dissection
Sangaku
SaRD Construction
SAS
Sawayama's Lemma
Scalar
Scalar product
Scalene triangle
Schlafli formula
Scintillating Grid Illusion
Scoring
Scoring MisÃ¨re
Scrub Tile Puzzle
Sealed Bids Method
Secant
- Secant
Secant Angles
Second Napoleon Point
Second Theorem of Apollonius
Sector (in circle)
See-Saw Lemma
Segment (in circle)
Self-conjugate triangle
Self-descriptive Strings
Self-documenting sentences
Self-dual configuration
Self-reference
Semigroup
Sending scouts into the desert
Separating point sets with a circle
Sequential Coalition
Sequential compactness
Sequential Rule
Set
Seven Circles Theorem
Seven Terms Periodic Sequence
Shaggy Dog Theorem
Shape Property
Shapes in a lattice
Shapes of constant width
- Star Construction of Shapes of Constant Width
Shapley-Shubik Index
Shearing Transform
Shepard's Parallelogram Illusion
Shift
Shimmer Illusion
Ship-Dock Theorem
Shredding the torus
Shuttle Puzzle
Sibling node
Sierpinski Carpet
Sierpinski gasket
- Dot Patterns and Sierpinski Gasket
- Sierpinski Gasket by Trema Removal
Sieve of Eratosthenes
Ïƒ-Algebra
Signed segment
Signum function, sign(t)
Silver Dollar Game
Similar orderings
Similar Triangles, theorem of
Similarity
Similarity dimension
Simple continued fraction
Simple graph
Simple polygon
Simplex
Simson Line
- Simson Line From Isogonal Perspective
Simson-Wallace Theorem
Simpson's paradox
Simultaneous Contrast Illusion
Simultaneous Contrast Illusion II
Sine Law
Single formula to express any integer with digits 0-9 each used just once
Six Circles Theorem (Elkies)
Six Circles Theorem (Evelyn)
Skolem Sequence
Slider Puzzles
Sliders
Slope
Slope-Intercept Equation of a Straight Line
Social Choice
Soddy circles
Soddy Line
Soddy points
Solitaire in the Circle
Somos-4 Sequence
Soriteses
Soroban
Sorting Algorithms
Spanning Tree
Sperner's Labeling
Sperner's Lemma
Sperner's Theorem
Sphere
Spieker Center
Spira Mirabilis
Spiral Similarity
- Miquel's Point of a 4-line Via Spiral Similarity
Splitter
Splitting piles
Sprague-Grundy function
Square
Square numbers
Squaring a circle
Squaring Parabola
Squares and Circles
Squares, Circles, and Triangles
Squinting Eyes Theorem
SSS
Stability
Staircase Illusion
Star Polygons
Star-shaped region
Stationary point
Steiner Porism
- Steiner Porism
Steiner's Circle
Steiner's Curve
Steiner's Theorem
Steiner's and Kirkman's Theorems
- Pascal Lines: Steiner and Kirkman Theorems II
Steinhaus' Problem
Stereographic projection
- Stereographic Projection and Radical Axes
Stern-Brocot Tree
- Binary Encoding with the Stern-Brocot tree
Stern's diatomic series
Stewart's theorem
Straight angle
Straight Edge Only Construction of Polar w.r.t. an Angle
Straight Edge Only Construction of Polar w.r.t. a Circle
Straight line
Straight Tromino
Strategy stealing in the game of Hex
Stretching
Suan pan
Subfactorial
Subgraph
Subgroup
Subjective contour
Subtraction Game
Successor
Sum Rule
Sums and Products
Superfactorial
Supergraph
Superposition Principle
Supplementary angles
Supporting lines of convex figures
Surjective function
Surreal numbers
- Surreal Numbers
- Surreal numbers and games
Syllogism, Modes Ponens
- Syllogism, more general
Symmedian
Symmedian point
Symmetric difference
Symmetric group
Symmetric relation
Symmetry in circle
Synthetic division
System of Distinct Representatives

3-4-5 triangle
3 glass puzzle
3 glass puzzle, second, more general tool
T-Junction
Take-Away Games
Tangent Pair
Tangent to two circles
Circle of Similitude
Tangential triangle
Tarski-Banach Decompositions
Taylor circle
Taylor series
Telescoping Series
Ternary number system
Tessellation
Tesseract
Thales' Theorem
Thales' Theorem

The only rational triangle
The Two Men of Tibet Problem
ThÃ©bault's Problem I
ThÃ©bault's Problem II
ThÃ©bault's Problem III
Theorem of Complete Quadrilateral
Theorem of Theaetetus
Thick set
Thin set
Third Proportional
Three pancakes problem
Three 3s
Three 4s
Three 5s
Three Circles and Common Tangents
Three circles problem
Three Tangents Theorem

Three Tangents Theorem

Toads And Frogs Puzzle
Toothpick Construction of a Square
Topological equivalence
Topological Space
Topological transformation
Topology
Torque
Torricelli point">
Torus
Totality (of a binary relation)
Totally ordered set
Tower of Hanoi

Sierpinski Gasket and Tower of Hanoi
Bicolor Towers of Hanoi

Toys and Tots problem
Trachoids
Train wheel quandary
Transcendental numbers
Transfinite Cardinality
Transitive groups
Transitivity in Action

Transivity

Translation Transform
Transpose of a vector
Transposition

What, how, and the Web

Transversal
Transverse gallop
Trapezoid
Tree
Trefoil knot
Trema
Triangle Classification
Triangle Inequality, the

Axioms of distance function
Absolute Value of Complex Number

Triangle of Similitude
Triangular Billiard
Triangular numbers

There exist triangular numbers that are also square

Triangulation

Diagonal Triangulation

Trichotomy, the law of
Trigonometric Form of Ceva's Theorem
Trigonometric Form of Complex Numbers
Trilateral Diagrams
Trilinear Coordinates
Trivial Ramsey Number
Tromino

Straight Tromino

Trot
Tucker Circles
Turn
Turning Turtles
Tweedledum & Tweedledee Principle
Twin Circles of Archimedes
Twisted Cord Illusion
Two Butterflies Theorem

Two Butterflies Theorem II

Two coins puzzle
Two Envelopes Paradox
Two Numbers Guessing Game
Two-squares identity

Uniform convergence
Uniform probability distribution
Union of sets
Unique Factorization Theorem
Uniqueness of number 30
Unit element
Unit Fraction
Unity
Universal Quantifier
UPC-A encoding
Urquhart's Theorem
- Urquhart's Theorem
V
- Value
- Van Obel Theorem, Determinants, and Barycentric Coordinates
  - Gergonne and Van Obel Theorems
- Van Aubel's theorem
- Van Schooten's theorem
  - Van Schooten's and Pompeiu's Theorems
- Varignon Parallelogram
- Vecten's Collinearity
- Vecten configuration
- Vecten Points
- Vector
- Vector product
- Vector Space
- Venn Diagrams
- Verging
- Versine
- Vertex
- Vertical Angles
- Viï¿½te's Formulas
- Viewing a Statue
- Viviani's Theorem
W
- Walk on a graph
- Wallace-Bolyai-Gerwien Theorem
- Wallace's Theorem
- Wasan
- Web poll
- Webster's Method of Apportionment
- Weierstrass-Bolzano property
- Weierstrass Product Inequality
- Weighted graph
- Weird curves bound normal areas
- WeitzenbÃ¶ck Inequality
- Well-ordered set
- What do you call a centipede?
- White's Illusion
- Whole number
- Whole part function, [x]
- Wilson's Theorem
- Wittenbauer's Parallelogram
- Word Ladders
- Word Problems
- Wunderlich's Plane Filling Curves
- Wundt Illusion
- Wundt Block Illusion
- Wythoff's Nim
- Wythoff's Nim II
X
- XOR
- X-intercept
Y
- Y Can't End in a Draw
- Y-intercept
- Y. Sawayama's Lemma
- Yosan
Z
- 0!=1
- Zaslavsky's theorem
- Zeckendorf's theorem
- Zenodorus Theorem
- Zero
- Zipf's Law
- ZÃ¶llner's Illusion

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