 thenumbertwentyone  Courtney Steketee
Blog posts, which date back to August, 2012, have included "Math Misconceptions Malady," "Classroom Tour," "#made4math #3," "Scoring Scales," "Group Behavior Logs," "Classroom Management," "Translating Words into Math," "Graphing Inequalities Day 2,"
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 The Theorem of Pythagoras  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. Several animated proofs of the Pythagorean theorem are presented, with applications to reallife problems
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 Theorem of the Day  Robin Whitty, London South Bank University
Every day, Whitty posts a PDF of a different theorem, lemma, law, formula, or identity  each "as selfcontained as possible." With pictorial interpretation; proof; glossary briefly explaining some parts of the mathematical language; references to related
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 Theoretical and Numerical Approach to "Magic Angle" of Stone Skipping  Shinichiro Nagahiro and Yoshinori Hayakawa, Department of Physics, Tohoku University, Japan
As published in the American Physical Society's Physical Review Letters: Nagahiro and Hayakawa "... investigate the condition for the bounce of circular disks which obliquely impacts on the fluid surface. An experiment [C. Clanet, F. Hersen, and L. Bocquet,
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 Theoretical Computer Science  Elsevier Science
The journal is mathematical and abstract in spirit, but derives its motivation from practical and everyday computation. Its aim is to understand the nature of computation and to provide more efficient methodologies. All papers introducing or studying
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 Theoretical Learning  Peter Moxhay
Information about a pilot project in Portland, Maine, public schools to adapt an approach developed in Russia for early math education (grades 13). Includes contact forms and request forms for Portland area parents to download trial math applets for
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 Theoretical Statistics  Peter Guttorp, University of Washington
A course intended for Ph.D. students in Statistics, Biostatistics, and other quantitative fields. Syllabus, handouts, research projects, homework problems.
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 Theory and Applications of Categories (TAC)
An electronic, refereed journal for articles that significantly advance the study of categorical algebra or methods, or that make significant new contributions to mathematical science using categorical methods. The scope of the journal includes: all areas
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 Theory and Applications of Categories (TAC)  Robert Rosebrugh, Ed.; Mount Allison University
The allelectronic, refereed journal on Category Theory, categorical methods and their applications in the mathematical sciences. The scope of the journal includes: all areas of pure category theory, including higher dimensional categories; applications
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 The Theory Group  University of St. Andrews, U.K.
The Theory Group investigates aspects of theoretical computer science including: specification; automated theorem proving techniques and applications (especially in computer algebra); computational logic, including logic programming and proof theory;
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 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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 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 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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 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
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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 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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