 Triangle Centers  Clark Kimberling; Dept. of Mathematics, Univ. of Evansville, Evansville, IN
A listing, with description and illustration, of 20thcentury triangle centers (including: Schiffler Point, Exeter Point, Parry Point, congruent isoscelizers point, Yff Center of Congruence, isoperimetric point and equal detour point, AjimaMalfatti Points,
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 Triangle Congruence  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about triangle congruences, such as "Why can't the SSA Theorem be used to prove congruence?" and "When should we use Congruent Parts Congruent Triangles Congruent (CPCTC), and how does it prove anything?"
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 Triangle Formulas (Ask Dr. Math FAQ)  Math Forum
Formulas for finding the area, perimeter, etc. of an equilateral, isosceles, right, or scalene triangle.
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 Triangle: Proof  Michal Wojcik
A proof that the sum of the angles in a triangle is 180 degrees. This page is written in HTML with two graphical images.
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 Triangle Puzzle  Evelyn Sander, Geometry Forum Archives, The Geometry Center
Pick an arbitrary point in the interior of an equilateral triangle. Now go halfway towards one of the three vertices (you get to pick which vertex). Now you are at a new point in the triangle. Again go halfway towards any vertex. Continue this process.
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 Triangles and Pyramids: Playing Math!  Hollis Easter
A "teachable" on the construction of freestanding pyramids made "by folding a single piece of paper, with only a single piece of tape to hold them together...." This blog post goes on to include photos of a net, diagrams, and "things to investigate":
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 Triangles and Simplices (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on triangles and their higherdimensional generalizations (simplices), with a particular interest in partitioning regions into triangles, tetrahedra, or higher dimensional simplices, for various applications
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 Triangles, Circles, And Waves  Kenny Felder
The site provides an overview of trigonometry. The material is merely
a refresher; only useful to beginners in trigonometry when used as supplementary course material in a trigonometry class.
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 Triangles in Elliptic Geometry  Thomas Banchoff, The Geometry Center
An examination of some properties of triangles in elliptic geometry, which for this purpose are equivalent to geometry on a hemisphere. The aim is to construct a quadrilateral with two right angles having area equal to that of a given spherical triangle.
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 Triangle with one 90degree Angle  NASA Lewis Learning Technologies Project
A triangle with one 90 degree angle is always: an equilateral triangle; an acute triangle; an obtuse triangle; or, a right triangle? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Triangular Numbers
Triangular and square numbers, presented with numeric, algebraic, and geometric illustrations, proofs, and formulas.
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 triangular prism  Manjit Singh Atwal
Download lessons and worksheets about triangular prisms, including finding surface areas and volumes.
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 Triangulation (SMILE)  Ann M. W. Brandon, Oak Forest High School
A lesson designed to teach students the basics of how to perform and calculate
triangulation. From the Practical and Applied Math section of a collection of almost 200 single concept lessons by the Science and Mathematics Initiative for Learning Enhancement.
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 Tribute to Invariance  Cut the Knot!, Alexander Bogomolny
As a competitive activity, the Squares and Circles game is not very challenging in itself. That is to say, the outcome of the game does not depend on how the game proceeds. The challenge is to come up with this realization and establish its veracity.
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 Tricki  Gowers, Timothy; Sisask, Olof; and Frolkin, Alex
A wiki "repository of mathematical knowhow" that encompasses techniques ranging from the very general to those that concern particular subareas of mathematics. Browse problemsolving ideas by technique: for finding algorithms and algorithmic proofs,
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 Tricks for Learning Math  Math Forum, Teacher2Teacher FAQ
Answers to a frequently asked question: What are some math tricks and mnemonic devices I can use with my students?
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 Tricky Crossings  Ivars Peterson (MathLand)
Have you heard the one about an itinerant entertainer traveling with a wolf, a goat, and a basket of cabbages? The showman comes to a river and finds a small boat that holds only himself and one passenger. For obvious reasons, he can't leave the wolf
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 Tricky Dice  Ivars Peterson (MathTrek)
The game involves four specially numbered dice. You let your opponent pick any one of the four dice. You choose one of the remaining three dice. Each player tosses his or her die, and the higher number wins the throw. Amazingly, in a game involving 10
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 Tricky Tables (MatheMUSEments!)  Ivars Peterson (Math Muse for Kids)
The shape of a billiard table has a lot to do with the types of shots you can make in a game of billiards. Which of the odd tables pictured do you think would be your best bet for hitting another ball? Suppose you have a circular table, or a rectangular
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 Trig According to Euclid  Len Smiley, Deborah Smiley
Four figures proving trigonometric addition and subtraction formulas for cosine and sine. Free of Cartesian coordinates, the proofs are synthetic and use a common, minimal diagram from Euclidean geometry.
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 Trigonometric Functions and Calculus  Waner, Costenoble; Hofstra University
A text on the WWW for liberal arts and business majors. Contents (each with exercises): Modeling with the Sine Function; The Six Trigonometric Functions; Derivatives of Trigonometric Functions; Integrals of Trigonometric Functions.
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 Trigonometric Functions  Larry Gladney, Dept. of Physics, Univ. of Pennsylvania
From the Interactive Textbook of PFP 96. A review of the trigonometric functions, sine, cosine, and tangent, as the most frequently used functions seen in introductory physics.
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 The Trigonometric Functions  MacTutor Math History Archives
Linked essay sketching trigonometry from its beginnings out of the early correspondence between astronomy and mathematics through the 18th century, with 17 references (books/articles).
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 Trigonometric Functions (SMILE)  Lesia Smith, Michael M. Byrne School
A lesson designed to teach students to define and demonstrate the six trigonometric functions; and to facilitate using the three most frequently used trigonometric functions. From the Algebra and Trigonometry section of a collection of almost 200 single
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 Trigonometric Identities  David Manura
Table of Common Angles, Law of Sines, Law of Cosines, and more.
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 Trigonometry and Calculus Problem of the Week  Math Forum
Trigonometry and calculus problems from a variety of sources, including textbooks, math contests, NCTM books, puzzle books, and reallife situations, designed to reflect different levels of difficulty. From 1998 until 2002, the goal was to challenge students
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 Trigonometry Challenge  ETCAI Products
A program designed to supplement your classroom and textbook instruction in numerical trigonometry. A trial program is available for download. The generic topics can be used with most textbooks. For Windows 95/98/98SE/me/XP/2000/NT4.
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 Trigonometry Formulas  Math Forum; Ask Dr. Math FAQ
Formulas for trig functions, bounds, identities, solving right and oblique triangles and inverse trig functions.
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 Trigonometry (Manipula Math)  International Educational Software (IES Inc.)
More than 20 Java applets designed to demonstrate principles of trigonometry, including sine, cosine, and tangent function boxes; graph of y=sin x, y=cos x,
y=sin ax, y=A sin (Bx+C), and y=sin x + cos x; Fourier series; sin t = a;
cos t=a; sin(A+B);
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 Trigonometry Reference Sheets (S.M.A.R.T.)  Math Share Shop
Basic curves. By students at Theodore Roosevelt H.S., Bronx, & Edward R. Murrow High School, Brooklyn.
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 Trigonometry (Seeing is Believing)  De Silva, D'Andreti; ThinkQuest 1997
A trigonometry tutorial, comprising: angles; trigonometric functions; oblique triangles; vectors; polar cordinates; complex numbers; and hyperbolic functions.
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 Trigonometry (S.O.S. Mathematics)  Dept. of Mathematical Sciences, Univ. of Texas at El Paso
An online course: learning units presented in worksheet format review the most important results, techniques and formulas in college and precollege trigonometry. Trigonometry: Angle Measures, Trigonometric Functions (magic identity, Addition Formulas,
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 Trigonometry Table  Industrial Press
Tables that give corresponding sine, cosine, tangent, secant, cosecant, and cotangent values for angles 0 to 90 degrees.
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 Trigonometry  Technical Tutoring
Site provides an introduction to trigonometry, includes illustrative examples and exercises in basic trigonometry as well as a summary of the important basic trig identities and formulae.
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 Trioker  Triominoes Puzzle  J. Marc Genevey
Le jeu de Trioker a été inventé par Monsieur Odier et étudié par luimême et son compère Mr Roussel dans leur ouvrage Surprenant Triangles. Il est composé de l'ensemble des 24 pièces triangulaires
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 Trisecting a Line Segment  Robert Styer
Several ways to trisect a line segment using compass and straightedge.
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 Trisecting an Angle  MacTutor Math History Archives
Linked essay tracing the history of the classical Greek problem of trisecting an
arbitrary angle using for the construction only ruler and compass (which is
impossible)  but, failing that, finding some other method.
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 Trisecting the Angle  Steven Dutch; University of Wisconsin  Green Bay
Why is trisecting an angle with a straightedge and compass impossible? Discussion includes several other proofs of impossibility (the largest prime number, the square root of 2, repeating patterns in the plane) and some alternate methods of trisection
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 Triumph of the Nerds: A History of the Computer  Robert X. Cringely; PBS Online
A companion Web site for the Public Broadcasting System television special hosted by Robert Cringely, "Triumph of the Nerds: The Rise of Accidental Empires." Learn how youthful amateurs, hippies, and selfproclaimed "nerds" accidentally changed the world.
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 Troublesome Weather Trends  Ivars Peterson (MathTrek)
In the February Bulletin of the American Meteorological Society, Statistician Kevin J. Coakley of the National Institute of Standards and Technology in
Boulder, Colo. argues that ... daily temperatures don’t vary randomly. They generally tend to rise
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 Trouble with WildCard Poker  Ivars Peterson (MathLand)
Poker originated in the Louisiana territory around the year 1800. Ever since, this addictive card game has occupied the time and teased the minds of generations of gamblers. It has also attracted the attention of mathematicians and statisticians. The
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 Truel in the Sun  Ivars Peterson (MathTrek)
Brilliant sunshine bakes a huddled row of ramshackle, weatherbeaten buildings lining a dusty thoroughfare. Two gunfighters slam out of a decrepit saloon and stalk toward their posts at either end of the street. Facing each other, they prepare to draw
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 Truncated Octahedron Blocks  Hop David
A discussion of a threedimensional tessellation that may make a good bridge between the rectangular solid tessellation and the octa/tetrahedral tessellation.
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 The Truth Tree's Math and Logic Board  Bob Scott, Ron Savori
A collection of math and logic problems, from Pascal's Pizza Parlor and Leaning Ladders to The Old Lady and the Eggs and The Rickety Table Disaster. Register to solve these and other problems and compete with other visitors to The Truth Tree.
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 TSM4: 'Using the Internet for Mathematics'  Oundle School, Peterborough, UK
A oneday conference for teachers held 11 May 1998 at Oundle School, Peterborough, UK. Technology for Secondary and College Mathematics (TSM) is a teacher training initiative based at Oundle School. Online Workshops: "How to download text and images off
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 The Tunnel of Samos  Project MATHEMATICS!, California Institute of Technology
A videotapeandworkbook module that explores a basic topic in high school mathematics in ways that cannot be done at the chalkboard or in a textbook. This video describes a remarkable engineering work of ancient times: excavating a onekilometer tunnel
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 Turbo Tables Educational Software  AGoGoGadget
Intended to teach multiplication techniques especially useful for products larger than 12x12. Includes teaching module, timed trial, and game for practicing your multiplication skills. Free demo available. Available for Windows XP and Pocket PC platforms.
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 TurkZeka  Yilmaz Ekici, TurkZeka.com
Clever puzzles, posted regularly, with quarterly puzzle competitions open to all with free login. In Turkish, English, and Japanese.
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 Turn of the Screw  Ivars Peterson (MathTrek)
Mathematician Chris Rorres of Drexel University in Philadelphia has taken a close look at Vitruvius's specifications for constructing an Archimedes screw... Recent years have seen a revival of interest in the Archimedes screw, particularly for its proven,
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 Turtle Tracks  Ivars Peterson (MathTrek)
One way to describe a geometric figure is in terms of the path generated by a moving point. Using the computer language LOGO, children can produce a list of commands to govern the motion of a "turtle" and trace out a geometric track on the computer screen.
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