 Theory of Tieknots  Yong Mao
The mathematical theory behind tying a necktie, with illustrations of the Four in Hand, the Pratt Knot, the HalfWindsor, and the FullWindsor, and a classification of necktie knots with respect to size and shape. Tying a tie knot is equivalent to a persistent
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 There are trisectable angles that are not constructible  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Why certain angles that are trisectable cannot be constructed by traditional methods.
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 There exist triangular numbers that are also square  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Inspired by a message sent in by Chris Whitrow, this page enumerates the set of infinite numbers that are concurrently triangular and square, and defines a recurrence relation for generating them.
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 There Is No Place Like SPACE  Sharon White
Junior high students explore living in space through this interdisciplinary (art, language arts, math, reading, social studies and science) project. Site contains a summary, scenario, student pages, and Internet links, as well as a list of standards addressed.
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 Thermicks  P. Zuidema
A Matlab routine for 2D thermal analysis.
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 Theron J. Hitchman
Scholarship and teaching by a professor of mathematics at the University of Northern Iowa. Hitchman's research focuses on differential and metric geometry, dynamical systems, and Lie theory, with particular interest in discrete subgroups of semisimple
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 These are Times that Try Mathematicians' Souls  David Brooks
Spurred by the Unabomber arrest, David Brooks, Science Editor, says it's time to stand on our desktops and shout to the world: "Say it out loud, I like math and I'm proud!" Previously published in The Telegraph (Nashua, NH).
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 The Theta Foundation
A scientific and notforprofit organisation, promoting mathematical knowledge, based in Romania.
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 TheXorb  Jagan Deb
Online calculators for the slope and yintercept of linear equations; standard deviations; mean, mode, and range; the Pythagorean Theorem; and properties of geometric figures such as triangles, squares, circles (circumference given area; area given diameter;
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 A Thing In Common  Cut the Knot!, Alexander Bogomolny
Two applets, both of which use the Pythagorean theorem: a puzzle (Draw an {N/D} star polygon  a polygon whose N vertices are uniformly distributed on a circle, but each vertex is connected to its Dth neighbor. Regular polygons correspond to D = 1, and
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 Things I Made From Yarn  Alan Eliasen
Futureboy's online calculators include a blackjack strategy table, a model solar system calculator (create your own model solar system of any scale), a sun locator (find current position of the sun), a historical currency converter (find out "how much
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 Things Impossible  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Essays on impossible things, including trisecting an angle, doubling a cube, squaring a circle, moving pegs five places in one direction (via checkerjumps), finding the center of a given circle with the straightedge alone, representing the square root
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 Think3d!  Allyson Hutton, Director
Inspired by an architect's visit to a 4th grade classroom, this elementary school curriculum develops spatial reasoning and visuospatial thinking through 2D to 3D transformation challenges in origami and popup paper engineering. Collaboration with
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 Think & Derive  Chris Long
Monthly mathematical columns from May 1994 through April 1996 written for Central New Jersey Mensa's Forvm. Problems and puzzles, many with solutions.
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 Thinkfinity  Verizon Foundation
Browse lesson plans by state or search them for keywords. Educational resources developed by Thinkfinity or by partners such as NCTM include interactive games, news, videos, webinars, worksheets, and calendars of birthdays and biographies.
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 ThinkFun  ThinkFun, Inc.
The makers of Spin Out and Rush Hour seek to "push [you] farther, probe deeper and think more creatively through game play." Brainteaser games include Math Dice, which challenges you to use addition, subtraction, multiplication, division, and exponents
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 Thinking Blocks  Colleen King, Math Advantage Learning Center
Thinking Blocks teaches students to visualize and model math word problems. The program features interactive exercises, video instruction, and independent practice, all online.
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 Thinking Fountain  Science Museum of Minnesota
Thinking Fountain offers surprising and personal connections to science. It's a living card file full of ideas and activities. Includes the opportunity to add your own projects. See Shapes Cluster: Shapes & Math: Shape Walk, I C Shapes, Bubble Geometry,
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 Thinking Fountain Shape Cluster  Science Museum of Minnesota
Activities, images, and experiments relating science, math, and language arts. The shapes and math cluster features shape walk, I C shapes (finding circles, squares, and triangles in everyday objects), soap bubble geometry, pyramids and cubes (building
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 Thinking Mathematically  Mark Chubb
Blog by a teacher and instructional coach in Canada. Posts, which date back to June, 2016, have included "Purposeful Practice: Happy Numbers"; "Concept vs Procedure: An anecdote about what it means to be good at math"; "Never Skip the Closing of the Lesson";
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 Thinking Mathematics!  James Tanton
Tanton writes wordless volumes of creative and surprising math puzzles, accessible approaches to calculus suitable for standardized test preparation, and curriculum "tidbits." Download his free guides to fractions and "to everything quadratic," and watch
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 Think Maths  Matt Parker
This group of mathematics speakers visits schools to perform maths talks and workshops in the UK. Sessions present math in ways that "grab the attention of students and remind them that maths is something to be enjoyed." Free downloads include domino
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 ThinkNum  Gregory Ugwi
A webbased financial data analysis engine. Use regression, curve trades, and other quantitative trading algorithms from scipy, numpy, and similar open source libraries to analyze economic information from hundreds of sources ranging from the ADO National
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 ThinkQuest
An international contest designed to encourage students from different schools and different backgrounds to work together in teams toward creating valuable educational tools on the Internet while enhancing their ability to communicate and cooperate in
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 ThinkThankThunk  Shawn Cornally
Blog by an Iowa headmaster and teacher of science, technology, engineering, and math (STEM). See, in particular, Cornally's collection of posts on StandardsBased Grading (SBG) and ongoing series on Honors Calculus course lessons, titled "Calculus: A
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 Think Through Math  Imagine Learning Inc.
Adaptive, differentiated curriculum to prepare students in third grade math through Algebra I classes prepare for the Common Core State Standards (CCSS). Watch Think Through Math (TTM) videos, request a demo, and more.
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 ThinkWave.com
A free web community that provides secure internetbased communication for parents, students, and teachers: realtime information about attendance, assignments, grades, and school curriculum.
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 Third Apex to Fractovia  Juan Luis Martínez
Several galleries, each with up to 18 fractal images, and discussions on fractals as art. Also an uptodate list of freeware fractal generators, screen savers, and fractal music software, with links and reviews.
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 Third Grade (AAA Math)  John Banfill
Interactive math exercises, lessons, and games covering basic math concepts and methods, for third grade.
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 Third International Mathematics and Science Study (TIMSS)  Initial Findings  National Center for Education Statistics (NCES)
Highlights from TIMSS; videotape classroom study report and classroom study; responses; the Commissioner's speech; results at the fourth, eighth, and twelfthgrade levels; test items, an annotated TIMSS publication list, and more. See also the 1999
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 Third International Mathematics and Science Study (TIMSS)  Math Forum
The Math Forum's page of resources on the TIMSS study. Initial findings, NCTM response, and more.
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 This is MegaMathematics! (MegaMath)  Nancy Casey; Los Alamos National Laboratory
The frontier of mathematics is an exciting place, where mathematicians experiment and play with creative and imaginative ideas, many of them accessible to young children; others (infinity is a good example) whose profound mathematical importance is not
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 This Is Statistics  American Statistical Association
Why study statistics? For students as well as their parents, teachers, and counselors, the American Statistical Association (ASA) provides a host of motives: to make a difference, have fun, satisfy curiosity, and make money, among other reasons. "Which
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 thnik again!  Jan Nordgreen
"Silly mathematical dialogues aimed to confuse." Nordgreen's daily blog of brain teasers and quotes dates back to November, 2007.
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 Thomas Harriot's manuscripts  MacTutor Math History Archives
Linked essay: Thomas Harriot died in 1621. He had published no mathematical or astronomical works during his lifetime, but he left his papers in reasonably good order and set out his wishes in his will that they should be properly edited and published.
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 Thom's Fractals
A collection of fractal creations: images and wallpaper tiles, and links.
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 Thorleif's SOMA page  Thorleif Bundgard, Denmark
Over a thousand figures for these cubes: standard figures (176, all solved); McFarrens figure set (798, all possible); and more. An index of all figures is available. With some SOMA history and a link to a newsletter.
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 Those Amazing Flying Mathematicians  Keith Devlin (Devlin's Angle)
October is the month when those of us living in the United States see migrating birds moving south for the winter. How do they know which direction to fly?... Assuming that the average bird is not the mathematical equivalent of a college math major, how
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 ThoughtBox  ThoughtBox Limited
Makers of Numerosity, the "gameful learning" arithmetic app for the iPad. Also available from thoughtbox.co and thoughtboxlearning.com.
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 Three Common Graphs  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about three common graphs: bar graphs, histograms, and pictograms.
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 Threedimensional Geometry (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on threedimensional geometry.
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 Three Dimensional Graphing Applet  James Goodenberger
A Java applet with which to graph first degree equations with three variables (planes) in three dimensions. The graph can be rotated and zoomed in or out of, but it won't graph a plane that passes through the origin.
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 Three Door Puzzle  Sky Coyote
In interactive page with an explanation of this classic, controversial problem, sometimes referred to as "Monty's Dilemma" or the "Game Show Problem." Links to a game simulation, the answer to problem, and an Ndoor generalization are provided.
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 Three for the Money: The Degree/Diameter Problem (MegaMath)  Nancy Casey; Los Alamos National Laboratory
Students can understand and work on an unsolved problem in mathematics. There is a good chance that this problem can be solved by someone who spends enough time experimenting with it. The only skills required to work on it are the ability to draw dots
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 Three Houses, Three Utilities  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
You are to draw a line from each house to each utility, without the lines ever crossing. Can you connect the houses to the utilities?
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 The Three Jugs Problem  Cut the Knot!, Alexander Bogomolny
Two friends who have an eightquart jug of water wish to share it evenly. They also have two empty jars, one holding five quarts, the other three. How can they each measure exactly 4 quarts of water? ... The description of the 3 Jugs problem as a triple
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 Three Skills For Algebra  Alan Selby
This book describes three skills key to the algebraic way of writing and thinking, offering a first image of mathematics beyond arithmetic. It also describes the first elements of logic or rulebased reason, needed in all disciplines for writing or a
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 Three Years Of Computing: Final Report on the Palindrome Quest  John Walker
"Pick a number. Reverse its digits and add the resulting number to the original number. If the result isn't a palindrome, repeat the process. Do all numbers in base 10 eventually become palindromes through this process? Nobody knows." The story of a
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 Three Years of Computing: Final Report On The Palindrome Quest  John Walker
A 1990 report on computations on the 196 problem: "Pick a number. Reverse its digits and add the resulting number to the original number. If the result isn't a palindrome, repeat the process. Do all numbers in base 10 eventually become palindromes through
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 Through Mazes to Mathematics  Tony Phillips; Dept. of Mathematics, SUNYStony Brook
Material about a class of mazes that have a complete mathematical description. Includes building your own labyrinth, an activity suitable for 4thgraders and up. Explores the relationship between mazes and mathematics. Examples and calculations with Simple,
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