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# Tetrahedron

In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons) is a polyhedron composed of four triangular faces, three of which meet at each corner or vertex. [1]

## Aerodrome

An aerodrome or airdrome is a location from which aircraft flight operations take place, regardless of whether they involve air cargo, passengers, or neither.

## Aerodynamics

Aerodynamics, from Greek ἀήρ aer (air) + δυναμική (dynamics), is a branch of Fluid dynamics concerned with studying the motion of air, particularly when it interacts with a solid object, such as an airplane wing.

## Alternating group

In mathematics, an alternating group is the group of even permutations of a finite set.

## Alternation (geometry)

In geometry, an alternation or partial truncation, is an operation on a polygon, polyhedron, tiling, or higher dimensional polytope that removes alternate vertices.

## American Mathematical Monthly

The American Mathematical Monthly is a mathematical journal founded by Benjamin Finkel in 1894.

## Ammonium

The ammonium cation is a positively charged polyatomic ion with the chemical formula NH4+.

## Antiprism

In geometry, an n-sided antiprism is a polyhedron composed of two parallel copies of some particular n-sided polygon, connected by an alternating band of triangles.

## Apex (geometry)

In geometry, an apex (Latin for 'summit, peak, tip, top, extreme end;') is the vertex which is in some sense the highest of the figure to which it belongs.

## Approximation

An approximation is anything that is similar but not exactly equal to something else.

## Area

Area is the quantity that expresses the extent of a two-dimensional figure or shape, or planar lamina, in the plane.

## Aristotle

Aristotle (Ἀριστοτέλης, Aristotélēs; 384322 BC) was a Greek philosopher and scientist born in the Macedonian city of Stagira, Chalkidice, on the northern periphery of Classical Greece.

## Artificial intelligence

Artificial intelligence (AI) is the intelligence exhibited by machines or software.

## Base (geometry)

In geometry, a base is a side of a polygon or face of a polyhedron, particularly one perpendicular to the direction height is measured or on what is considered to the bottom of the object.

## Bisection

In geometry, bisection is the division of something into two equal or congruent parts, usually by a line, which is then called a bisector.

## Boerdijk–Coxeter helix

The Boerdijk–Coxeter helix, named after H. S. M. Coxeter and A. H. Boerdijk, is a linear stacking of regular tetrahedra, arranged so that the edges of the complex that belong to a single tetrahedron form three intertwined helices.

## Caltrop

A caltrop (also known as caltrap, galtrop, cheval trap, galthrap, galtrap, Jackrock calthrop or crow's footBattle of Alesia (Caesar's conquest of Gaul in 52 BC)), Battlefield Detectives program, (2006), rebroadcast: 2008-09-08 on History Channel International (13;00-14:00 hrs EDST); Note: No mention of name caltrop at all, but illustrated and given as battle key to defend Roman lines of circumvaliation per recent digs evidence.

## Cartesian coordinate system

A Cartesian coordinate system is a coordinate system that specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances from the point to two fixed perpendicular directed lines, measured in the same unit of length.

## Central angle

A central angle is an angle whose apex (vertex) is the center O of a circle and whose legs (sides) are radii intersecting the circle in two distinct points A and B thereby subtending an arc between those two points whose angle is (by definition) equal to that of the central angle itself.

## Centroid

In mathematics and physics, the centroid or geometric center of a two-dimensional region is the arithmetic mean ("average") position of all the points in the shape.

## Cevian

In geometry, a cevian is any line segment in a triangle with one endpoint on a vertex of the triangle and the other endpoint on the opposite side.

## Chemical engineering

Chemical engineering is a branch of engineering that applies physical sciences (e.g. chemistry and physics) and life sciences (e.g. biology, microbiology and biochemistry) together with mathematics and economics to produce, transform, transport, and properly use chemicals, materials and energy.

## Circumscribed sphere

In geometry, a circumscribed sphere of a polyhedron is a sphere that contains the polyhedron and touches each of the polyhedron's vertices.

## Civil engineering

Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings.

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## Compound of five tetrahedra

The compound of five tetrahedra is one of the five regular polyhedral compounds.

## Compound of ten tetrahedra

The compound of ten tetrahedra is one of the five regular polyhedral compounds.

## Computational fluid dynamics

Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical analysis and algorithms to solve and analyze problems that involve fluid flows.

## Concurrent lines

In geometry, three or more lines in a plane or higher-dimensional space are said to be concurrent if they intersect at a single point.

## Conformal map

In mathematics, a conformal map is a function that preserves angles locally.

## Congruence (geometry)

In geometry, two figures or objects are congruent if they have the same shape and size, or if one has the same shape and size as the mirror image of the other.

## Conjugacy class

In mathematics, especially group theory, the elements of any group may be partitioned into conjugacy classes; members of the same conjugacy class share many properties, and study of conjugacy classes of non-abelian groups reveals many important features of their structure.

## Convex polytope

A convex polytope is a special case of a polytope, having the additional property that it is also a convex set of points in the n-dimensional space Rn.

## Covalent bond

A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.

## Coxeter element

In mathematics, the Coxeter number h is the order of a Coxeter element of an irreducible Coxeter group.

## Coxeter notation

In geometry, Coxeter notation (also Coxeter symbol) is a system of classifying symmetry groups, describing the angles between with fundamental reflections of a Coxeter group in a bracketed notation, with modifiers to indicate certain subgroups.

## Cross product

In mathematics and vector calculus, the cross product or vector product (occasionally directed area product to emphasize the geometric significance) is a binary operation on two vectors in three-dimensional space (R3) and is denoted by the symbol ×. The cross product a × b of two linearly independent vectors a and b is a vector that is perpendicular to both and therefore normal to the plane containing them.

## Crystal

A crystal or crystalline solid is a solid material whose constituents, such as atoms, molecules or ions, are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions.

## Cube

In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets or sides, with three meeting at each vertex.

## Cyclic group

In algebra, a cyclic group is a group that is generated by a single element.

## Degrees of freedom (statistics)

In statistics, the number of degrees of freedom is the number of values in the final calculation of a statistic that are free to vary.

## Demihypercube

In geometry, demihypercubes (also called n-demicubes, n-hemicubes, and half measure polytopes) are a class of n-polytopes constructed from alternation of an n-hypercube, labeled as h&gamma;n for being half of the hypercube family, &gamma;n.

## Determinant

In linear algebra, the determinant is a useful value that can be computed from the elements of a square matrix.

## Dice

Dice (singular die or dice; from Old French dé; from Latin datum "something which is given or played"; plural dice or occasionally dices) are small throwable objects with multiple resting positions, used for generating random numbers.

## Digon

In geometry, a digon, bigon, biangle or 2-gon is a polygon with two sides (edges) and two vertices.

## Dihedral angle

In geometry, a dihedral or torsion angle is the angle between two hyperplanes.

## Disphenoid

In geometry, a disphenoid (also bisphenoid) (from Greek sphenoeides, "wedgelike") is a tetrahedron whose four faces are congruent acute-angled triangles.

## Distance geometry problem

The distance geometry problem is the characterization and study of sets of points based only on given values of the distances between member pairs.

## Distance-regular graph

In mathematics, a distance-regular graph is a regular graph such that for any two vertices v and w, the number of vertices at distance j from v and at distance k from w depends only upon j, k, and i.

## Distance-transitive graph

In the mathematical field of graph theory, a distance-transitive graph is a graph such that, given any two vertices v and w at any distance i, and any other two vertices x and y at the same distance, there is an automorphism of the graph that carries v to x and w to y.

## Dodecahedron

In geometry, a dodecahedron (Greek δωδεκάεδρον, from δώδεκα dōdeka "twelve" + ἕδρα hédra "base", "seat" or "face") is any polyhedron with twelve flat faces.

## Dot product

In mathematics, the dot product or scalar product (sometimes inner product in the context of Euclidean space, or rarely projection product for emphasizing the geometric significance), is an algebraic operation that takes two equal-length sequences of numbers (usually coordinate vectors) and returns a single number.

## Dual polyhedron

In geometry, polyhedra are associated into pairs called duals, where the vertices of one correspond to the faces of the other.

## Edge (geometry)

In geometry, an edge is a particular type of line segment joining two vertices in a polygon, polyhedron, or higher-dimensional polytope.

## Electromagnetic field

An electromagnetic field (also EMF or EM field) is a physical field produced by electrically charged objects.

## Equilateral triangle

In geometry, an equilateral triangle is a triangle in which all three sides are equal.

## Euclidean geometry

Euclidean geometry is a mathematical system attributed to the Alexandrian Greek mathematician Euclid, which he described in his textbook on geometry: the Elements.

## Euler line

In geometry, the Euler line, named after Leonhard Euler, is a line determined from any triangle that is not equilateral.

## Exsphere (polyhedra)

In geometry, the exsphere of a face of a regular polyhedron is the sphere outside the polyhedron which touches the face and the planes defined by extending the adjacent faces outwards.

## Face (geometry)

In solid geometry, a face is a flat (planar) surface that forms part of the boundary of a solid object; a three-dimensional solid bounded exclusively by flat faces is a polyhedron.

## Finite element method

In mathematics, the finite element method (FEM) is a numerical technique for finding approximate solutions to boundary value problems for partial differential equations.

## Flexagon

In geometry, flexagons are flat models, usually constructed by folding strips of paper, that can be flexed or folded in certain ways to reveal faces besides the two that were originally on the back and front.

## Fluorescent lamp

A fluorescent lamp or a fluorescent tube is a low pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light.

## Four-sided die

Four-sided dice, abbreviated d4, are often used in tabletop role-playing games to obtain random integers in the range 1–4.

## Futurama

Futurama is an American adult animated science fiction sitcom created by Matt Groening for the Fox Broadcasting Company.

## Gaspard Monge

Gaspard Monge, Comte de Péluse (9 May 1746 – 28 July 1818) was a French mathematician, the inventor of descriptive geometry (the mathematical basis of technical drawing), and the father of differential geometry.

## Geometry

Geometry (from the γεωμετρία; geo- "earth", -metron "measurement") is a branch of mathematics concerned with questions of shape, size, relative position of figures, and the properties of space.

## Graph (mathematics)

In mathematics, and more specifically in graph theory, a graph is a representation of a set of objects where some pairs of objects are connected by links.

## Graph theory

In mathematics and computer science, graph theory is the study of graphs, which are mathematical structures used to model pairwise relations between objects.

## HAL 9000

HAL 9000 is a fictional character in Arthur C. Clarke's Space Odyssey series.

## Hamiltonian path

In the mathematical field of graph theory, a Hamiltonian path (or traceable path) is a path in an undirected or directed graph that visits each vertex exactly once.

## Handedness

Handedness is a better (faster or more precise) performance or individual preference for use of a hand.

## Harold Scott MacDonald Coxeter

Harold Scott MacDonald "Donald" Coxeter, FRS, FRSC, (February 9, 1907 &ndash; March 31, 2003) was a British-born Canadian geometer.

## Heron's formula

In geometry, Heron's formula (sometimes called Hero's formula) is named after Hero of Alexandria and states that the area of a triangle whose sides have lengths a, b, and c is where s is the semiperimeter of the triangle; that is, Heron's formula can also be written as Heron's formula is distinguished from other formulas for the area of a triangle, such as half the base times the height or half the modulus of a cross product of two sides, by requiring no arbitrary choice of side as base or vertex as origin.

## Hill tetrahedron

In geometry, the Hill tetrahedra are a family of space-filling tetrahedra.

## Honeycomb (geometry)

In geometry, a honeycomb is a space filling or close packing of polyhedral or higher-dimensional cells, so that there are no gaps.

## Hyperbolic space

In mathematics, hyperbolic space is a homogeneous space that has a constant negative curvature, where in this case the curvature is the sectional curvature.

## Incircle and excircles of a triangle

In geometry, the incircle or inscribed circle of a triangle is the largest circle contained in the triangle; it touches (is tangent to) the three sides.

## Inscribed sphere

In geometry, the inscribed sphere or insphere of a convex polyhedron is a sphere that is contained within the polyhedron and tangent to each of the polyhedron's faces.

## K-vertex-connected graph

In graph theory, a connected graph G is said to be k-vertex-connected (or k-connected) if it has more than k vertices and remains connected whenever fewer than k vertices are removed.

## Klein four-group

In mathematics, the Klein four-group (or just Klein group or Vierergruppe (four-group), often symbolized by the letter V or as K4) is the group, the direct product of two copies of the cyclic group of order 2.

## Law of sines

In trigonometry, the law of sines, sine law, sine formula, or sine rule is an equation relating the lengths of the sides of any shaped triangle to the sines of its angles.

## Lone pair

In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atomIUPAC Gold Book definition: and is sometimes called a non-bonding pair.

## Martina Schettina

Martina Schettina (born 1961) is an Austrian artist.

## Marvin Minsky

Marvin Lee Minsky (born August 9, 1927) is an American cognitive scientist in the field of artificial intelligence (AI), co-founder of the Massachusetts Institute of Technology's AI laboratory, and author of several texts on AI and philosophy.

## Mathematics Magazine

Mathematics Magazine is a refereed bimonthly publication of the Mathematical Association of America.

## Median (geometry)

In geometry, a median of a triangle is a line segment joining a vertex to the midpoint of the opposing side.

## Methane

Methane is a chemical compound with the chemical formula (one atom of carbon and four atoms of hydrogen).

## Midsphere

In geometry, the midsphere or intersphere of a polyhedron is a sphere which is tangent to every edge of the polyhedron.

## Mirror image

A mirror image (in a plane mirror) is a reflected duplication of an object that appears almost identical, but is reversed in the direction perpendicular to the mirror surface.

## Monolith (Space Odyssey)

Monoliths are fictional advanced machines built by an unseen extraterrestrial species that are described in Arthur C. Clarke's Space Odyssey series of novels and films.

## Mudvayne

Mudvayne is an American heavy metal band known for its sonic experimentation, innovative album art, face and body paint, masks and uniforms.

## Murakami–Yano formula

In geometry, the Murakami–Yano formula, introduced by, is a formula for the volume of a hyperbolic or spherical tetrahedron given in terms of its dihedral angles.

## N-skeleton

In mathematics, particularly in algebraic topology, the of a topological space X presented as a simplicial complex (resp. CW complex) refers to the subspace Xn that is the union of the simplices of X (resp. cells of X) of dimensions In other words, given an inductive definition of a complex, the is obtained by stopping at the.

## Naval architecture

Naval architecture also known as naval engineering, is an engineering discipline dealing with the engineering design process, shipbuilding, maintenance, and operation of marine vessels and structures.

## Net (polyhedron)

In geometry the net of a polyhedron is an arrangement of edge-joined polygons in the plane which can be folded (along edges) to become the faces of the polyhedron.

## Niccolò Fontana Tartaglia

Niccolò Fontana Tartaglia (1499/1500, Brescia &ndash; 13 December 1557, Venice) was an Italian mathematician, engineer (designing fortifications), a surveyor (of topography, seeking the best means of defense or offense) and a bookkeeper from the then-Republic of Venice (now part of Italy).

## Nine-point circle

In geometry, the nine-point circle is a circle that can be constructed for any given triangle.

## Numerical analysis

Numerical analysis is the study of algorithms that use numerical approximation (as opposed to general symbolic manipulations) for the problems of mathematical analysis (as distinguished from discrete mathematics).

## Oblivion (2013 film)

Oblivion is a 2013 post-apocalyptic science fiction film based on Joseph Kosinski's unpublished graphic novel of the same name.

## Octahedron

In geometry, an octahedron (plural: octahedra) is a polyhedron with eight faces.

## Orbifold notation

In geometry, orbifold notation (or orbifold signature) is a system, invented by William Thurston and popularized by the mathematician John Conway, for representing types of symmetry groups in two-dimensional spaces of constant curvature.

## Origami

) is the art of paper folding, which is often associated with Japanese culture.

## Orthocentric tetrahedron

In geometry, an orthocentric tetrahedron is a tetrahedron where all three pairs of opposite edges are perpendicular.

## Orthographic projection

Orthographic projection (or orthogonal projection) is a means of representing a three-dimensional object in two dimensions.

## Parallelepiped

In geometry, a parallelepiped is a three-dimensional figure formed by six parallelograms (the term rhomboid is also sometimes used with this meaning).

## Partial differential equation

In mathematics, a partial differential equation (PDE) is a differential equation that contains unknown multivariable functions and their partial derivatives.

## Perpendicular

In elementary geometry, the property of being perpendicular (perpendicularity) is the relationship between two lines which meet at a right angle (90 degrees).

## Piero della Francesca

Piero della Francesca (c. 1415 – 12 October 1492) was an Italian painter of the Early Renaissance.

## Planar graph

In graph theory, a planar graph is a graph that can be embedded in the plane, i.e., it can be drawn on the plane in such a way that its edges intersect only at their endpoints.

## Platonic graph

In the mathematical field of graph theory, a Platonic graph is a graph that has one of the Platonic solids as its skeleton.

## Platonic solid

In three-dimensional space, a Platonic solid is a regular, convex polyhedron.

## Point groups in three dimensions

In geometry, a point group in three dimensions is an isometry group in three dimensions that leaves the origin fixed, or correspondingly, an isometry group of a sphere.

## Point reflection

Not to be confused with inversive geometry, in which inversion is through a circle instead of a point. In geometry, a point reflection or inversion in a point (or inversion through a point, or central inversion) is a type of isometry of Euclidean space.

## Polygon

In elementary geometry, a polygon is a plane figure that is bounded by a finite chain of straight line segments closing in a loop to form a closed chain or circuit.

## Polygon mesh

A polygon mesh is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling.

## Polyhedron

In elementary geometry, a polyhedron (plural polyhedra or polyhedrons) is a solid in three dimensions with flat polygonal faces, straight edges and sharp corners or vertices.

## Polytope compound

A polyhedral compound is a figure that is composed of several polyhedra sharing a common centre.

## Projection (linear algebra)

In linear algebra and functional analysis, a projection is a linear transformation P from a vector space to itself such that.

## Pyramid (geometry)

In geometry, a pyramid is a polyhedron formed by connecting a polygonal base and a point, called the apex.

## Pyraminx

The Pyraminx is a regular tetrahedron puzzle in the style of Rubik's Cube.

## Pyramorphix

The Pyramorphix (often misspelt Pyramorphinx) is a tetrahedral puzzle similar to the Rubik's Cube.

## Quaternions and spatial rotation

Unit quaternions, also known as versors, provide a convenient mathematical notation for representing orientations and rotations of objects in three dimensions.

## Rectification (geometry)

In Euclidean geometry, rectification or complete-truncation is the process of truncating a polytope by marking the midpoints of all its edges, and cutting off its vertices at those points.

## Regular graph

In graph theory, a regular graph is a graph where each vertex has the same number of neighbors; i.e. every vertex has the same degree or valency.

## Regular Polytopes (book)

Regular Polytopes is a mathematical geometry book written by Canadian mathematician H.S.M. Coxeter.

## Resistor

A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element.

## Rhombohedron

In geometry, a rhombohedron is a three-dimensional figure like a cube, except that its faces are not squares but rhombi.

## Right angle

In geometry and trigonometry, a right angle is an angle that bisects the angle formed by two halves of a straight line.

## Role-playing

Role-playing refers to the changing of one's behaviour to assume a role, either unconsciously to fill a social role, or consciously to act out an adopted role.

## Royal Game of Ur

The Royal Game of Ur, also known as the Game of Twenty Squares, refers to an ancient game represented by two gameboards found in the Royal Tombs of Ur in Iraq by Sir Leonard Woolley in the 1920s.

## Rubik's Cube

Rubik's Cube is a 3-D combination puzzle invented in 1974 by Hungarian sculptor and professor of architecture Ernő Rubik.

## Schläfli orthoscheme

In geometry, Schläfli orthoscheme is a type of simplex.

## Schläfli symbol

In geometry, the Schläfli symbol is a notation of the form that defines regular polytopes and tessellations.

## Schoenflies notation

The Schoenflies (or Schönflies) notation, named after the German mathematician Arthur Moritz Schoenflies, is one of two conventions commonly used to describe point groups.

## Semiconductor

A semiconductor material has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass.

## Silicon

Silicon is a chemical element with symbol Si and atomic number 14.

## Simplex

In geometry, a simplex (plural: simplexes or simplices) is a generalization of the notion of a triangle or tetrahedron to arbitrary dimensions.

## Skew lines

In three-dimensional geometry, skew lines are two lines that do not intersect and are not parallel.

## Slope

In mathematics, the slope or gradient of a line is a number that describes both the direction and the steepness of the line.

## Solder

Solder (or in North America) is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece(s).

## Solid angle

In geometry, a solid angle (symbol: Ω) is the two-dimensional angle in three-dimensional space that an object subtends at a point.

## Solid-state electronics

Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material.

## Space frame

In architecture and structural engineering, a space frame or space structure is a truss-like, lightweight rigid structure constructed from interlocking struts in a geometric pattern.

## Spherical geometry

Spherical geometry is the geometry of the two-dimensional surface of a sphere.

## Spherical polyhedron

In mathematics, a spherical polyhedron or spherical tiling is a tiling of the sphere in which the surface is divided or partitioned by great arcs into bounded regions called spherical polygons.

## Spieker circle

In geometry, the incircle of the medial triangle of a triangle is the Spieker circle, named after 19th-century German geometer Theodor Spieker.

## Stanley Kubrick

Stanley Kubrick (July 26, 1928 – March 7, 1999) was an American film director, screenwriter, producer, cinematographer, editor and photographer.

## Stellated octahedron

The stellated octahedron, or stella octangula, is the only stellation of the octahedron.

The steradian (symbol: sr) or square radian is the SI unit of solid angle.

## Stereographic projection

In geometry, the stereographic projection is a particular mapping (function) that projects a sphere onto a plane.

## Symmetric graph

In the mathematical field of graph theory, a graph G is symmetric (or arc-transitive) if, given any two pairs of adjacent vertices u1—v1 and u2—v2 of G, there is an automorphism such that In other words, a graph is symmetric if its automorphism group acts transitively upon ordered pairs of adjacent vertices (that is, upon edges considered as having a direction).

## Symmetric group

In abstract algebra, the symmetric group Sn on a finite set of n symbols is the group whose elements are all the permutation operations that can be performed on n distinct symbols, and whose group operation is the composition of such permutation operations, which are defined as bijective functions from the set of symbols to itself.

## Symmetry group

In abstract algebra, the symmetry group of an object (image, signal, etc.) is the group of all transformations under which the object is invariant with composition as the group operation.

## Symmetry in mathematics

Symmetry occurs not only in geometry, but also in other branches of mathematics.

## Symmetry number

The symmetry number or symmetry order of an object is the number of different but indistinguishable (or equivalent) arrangements (or views) of the object, i.e. the order of its symmetry group.

## Table of polyhedron dihedral angles

The dihedral angles for the edge-transitive polyhedra are.

## Tangent

In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point.

## Telecommunications engineering

Telecommunications engineering, or telecom engineering, is an engineering discipline that brings together electrical engineering with computer science to enhance telecommunication systems.

## Tetra Pak

Tetra Pak is a multinational food packaging and processing company of Swedish origin with head offices in Lund, Sweden, and Lausanne, Switzerland.

## Tetragonal disphenoid honeycomb

The tetragonal disphenoid tetrahedral honeycomb is a space-filling tessellation (or honeycomb) in Euclidean 3-space made up of identical tetragonal disphenoidal cells.

## Tetrahedral hypothesis

The Tetrahedral hypothesis is an obsolete scientific theory attempting to explain the arrangement of the Earth's continents and oceans by referring to the geometry of a tetrahedron.

## Tetrahedral kite

This kite was invented by Alexander Graham Bell.

## Tetrahedral molecular geometry

In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron.

## Tetrahedral number

A tetrahedral number, or triangular pyramidal number, is a figurate number that represents a pyramid with a triangular base and three sides, called a tetrahedron.

## Tetrahedral-octahedral honeycomb

The tetrahedral-octahedral honeycomb, alternated cubic honeycomb is a space-filling tessellation (or honeycomb) in Euclidean 3-space.

## Tetrahedron

In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons) is a polyhedron composed of four triangular faces, three of which meet at each corner or vertex.

## Tetrahedron (journal)

Tetrahedron is a weekly peer-reviewed scientific journal covering the field of organic chemistry.

## Tetrahedron packing

In geometry, tetrahedron packing is the problem of arranging identical regular tetrahedra throughout three-dimensional space so as to fill the maximum possible fraction of space.

## The End of All Things to Come

The End of All Things to Come is the second studio album by the American heavy metal band Mudvayne.

## The Legend of Zelda

is a high-fantasy, action-adventure video game series created by Japanese game designers Shigeru Miyamoto and Takashi Tezuka.

## Trapezohedron

The n-gonal trapezohedron, antidipyramid or deltohedron is the dual polyhedron of an n-gonal antiprism.

## Triangle

A triangle is a polygon with three edges and three vertices.

## Triangular bipyramid

In geometry, the triangular bipyramid (or dipyramid) is a type of hexahedron, being the first in the infinite set of face-transitive bipyramids.

## Triforce

The is the golden triangle from Nintendo's ''The Legend of Zelda'' series of video games.

## Triple product

In vector calculus, a branch of mathematics, the triple product is a product of three 3-dimensional vectors, usually Euclidean vectors.

## Trirectangular tetrahedron

In geometry, a trirectangular tetrahedron is a tetrahedron where all three face angles at one vertex are right angles.

## Trivial group

In mathematics, a trivial group is a group consisting of a single element.

## Uniform polyhedron

A uniform polyhedron is a polyhedron which has regular polygons as faces and is vertex-transitive (transitive on its vertices, isogonal, i.e. there is an isometry mapping any vertex onto any other).

## Valence (chemistry)

In chemistry, the valence (or valency) of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules.

## Vertex (geometry)

In geometry, a vertex (plural vertices) is a special kind of point that describes the corners or intersections of geometric shapes.

## Vertex figure

In geometry a vertex figure is, broadly speaking, the figure exposed when a corner of a polyhedron or polytope is sliced off.

## Volume

Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance (solid, liquid, gas, or plasma) or shape occupies or contains.

## Wacław Sierpiński

Wacław Franciszek Sierpiński (March 14, 1882 – October 21, 1969) was a Polish mathematician.

## Water

Water (chemical formula: H2O) is a transparent fluid which forms the world's streams, lakes, oceans and rain, and is the major constituent of the fluids of organisms.

## Wheel graph

In the mathematical discipline of graph theory, a wheel graph Wn is a graph with n vertices (n ≥ 4), formed by connecting a single vertex to all vertices of an (n-1)-cycle.

## William Lowthian Green

William Lowthian Green (1819–1890) was an English adventurer and merchant, who later became cabinet minister in the Kingdom of Hawaii.

## 2001: A Space Odyssey (film)

2001: A Space Odyssey is a 1968 epic science fiction film produced and directed by Stanley Kubrick.

## 5-cell

In geometry, the 5-cell is a four-dimensional object bounded by 5 tetrahedral cells.

## References

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