 Circles of Dissonance  Ivars Peterson (MathTrek)
Much of today's music rests upon ancient tradition going back thousands of years to the time of the Greek mathematician and mystic Pythagoras. The Pythagoreans observed that tones an octave apart are pleasing to the ear. In modern terms,
one can say
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 Circles of Light: The Mathematics of Rainbows  Steven Janke; The Geometry Center
How are rainbows formed? Why do they only occur when the sun is behind the observer? If the sun is low on the horizon, at what angle in the sky should we expect to see a rainbow? This lab helps to answer these and other questions by examining a mathematical
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 Circle Zap  Michael Bulmer
A Java applet that gathers data on your ability to use a mouse rapidly and accurately, with suggested questions for classroom activities.
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 Circumference of an Ellipse (Ask Dr. Math FAQ)  Math Forum
A discussion of the derivation of the formula for the circumference of an ellipse. Also discussions of the evaluation of the formula, and approximating the circumference.
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 Citizen Maths  Ufi Charitable Trust
Free courses of selfpaced video tutorials, discussions, and handson activities to try out. Developed by Calderdale College (UK), with CogBooks, the Institute of Education, and Oxford Cambridge RSA (OCR).
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 CK12
Providers of free, standardsaligned, open content in the STEM subjects. See, in particular, the CK12 Foundation's flexbooks: customizable, free, curriculumaligned K12 math textbooks. In addition to dozens of student editions, some math flexbooks feature
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 ClarisWorks Graphing: Spreadsheet Lessons  Suzanne Alejandre
Stepbystep directions for using ClarisWorks spreadsheets, helpful in exploring the differences between exponential functions and linear functions. Bar graphs, pie charts, pictograms, and other graphs for linear, polynomial, and exponential functions.
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 Clash of the Chess Titans  Keith Devlin (Devlin's Angle)
Thoughts on the KasparovDeep Blue match of 3 May 1997. Throughout history, people have been building machines that can perform tasks better than humans. When Kasparov, referring to his upcoming match, talks about "an area that defines human beings,"
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 Class2Class  Melanie Sprouse
Class2Class is a clearinghouse designed to facilitate student and class participation in Internet projects, including collaborative projects, datacollecting experiments, peer tutoring, and keypal exchanges designed to enhance the mathematics in your
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 class.com  Class.com, Inc
Class.com provides distance education over the Internet, and offers a complete high school diploma from a fully accredited, universitybased independent study high school. Math course listings include a math skill review, basic mathematics, beginning
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 Classic Fallacies  Philip Spencer; University of Toronto Mathematics Network
Mathematical "proofs" demonstrating, among other things, that 1 = 2 and that all people in Canada are the same age. Each consists of several steps, and users search for the flaws. For every step there is explanation of why the flaw is or is not in that
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 Classic Problems  Math Forum; Ask Dr. Math FAQ
Classic problems from the Ask Dr. Math FAQ (Frequently Asked Questions) files, including: age word problems, birthday probability, boy or girl?, camel and bananas, coin problems, doubling pennies, grazing animals, liars and truthtellers, the missing dollar,
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 Classifying Numbers  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about classifying numbers, such as "How are the different types of numbers related?" and "What is a real number?"
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 Classroom Capsules and Notes  MAA Online
Classroom Capsules and Notes brings together the best of 114 years of the short classroom materials from the MAA print publications. These materials are free to everyone.
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 Classroom Compass  Adams, Powell, Assoc. Editors; Southwest Educational Development Laboratory
A magazine published from 1994 to 2005, with ideas, activities, and resources for teachers interested in improving instruction in science and mathematics, and links to simple classroom activities with ideas about learning and instruction. Each issue presents
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 Classroom Projects  TEAMS Distance Learning, Los Angeles County Office of Education (LACOE)
A site for teachers looking for a content area project or contest for the classroom. Join a TEAMS project or browse a list of projects and contests sponsored by other organizations. Extensive list of upcoming, current, ongoing, and completed projects
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 ClassZone  McDougal Littell, Publishers
In ClassZone, McDougal Littell has gathered together all of its activities, interactive online resources, research links, chapter quizzes, and other materials that support its popular middle and high school mathematics textbooks, such as Integrated Math
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 Clear Educational Solutions  Calvin Leung
Product and order information for InstaGraphs, PostIt Notes® printed with a grid for use as graph paper. Also includes a student survey and suggestions for using InstaGraphs as a fundraiser.
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 Cleave Books
Teacher Resources on Line (TRoL) include downloadable grid paper; Ttiles; dictionary exercises; shapes Bingo; MisMaths, an annotated collection of innumeracy and other math mistakes in news headlines; fact sheets; tables; formulas; a mathematical vocabulary
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 Click and Climb: Online Math Tutoring and Homework Help  ClickandClimb.com
Online math tutoring and math homework help resource. Professional tutors work with you oneonone using interactive whiteboard technology and VOIP (Skype) for audio. Tutoring is offered in grades 312 at your pace. You'll need a computer with high speed
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 Clickmazes  Gilbert, Mitchell
An extensive collection of interactive puzzles and mazes organized in the following categories: Maze gallery; Attic gallery; Maze of Life; HexaRoll; Oskar's fourbit mazes; 2D tilt mazes; Colourzone mazes; 3D tilt mazes; Tilt puzzles; NEWS and RULES;
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 The CliffHanger (MSTE)  Nicholas Exner; University of Illinois at UrbanaChampaign (UIUC)
A Java simulation of statistics and probability. From where he stands, one step toward the cliff would send poor Homer Simpson over the edge. He takes random steps, either toward or away from the cliff. At any step his probability of taking a step away
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 Climate Classroom  One Million Acts of Green
This curriculum encourages students to analyze the science of global warming and its relevance to current events and their daily lives, through classroom activities, lesson plans, and family and community activities. The One Million Acts of Green Program
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 CLKCalculator  Lars Kobarg
Reverse Polish notation Calcualtor is a calculator program for Windows with unit conversion and matrix calculator, functions for vectors and complex numbers, and a
function plotter.
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 CLKCalculator  Lars Kobarg
A skinnable calculator for Windows, intended for a wide range of users. Use algebraic or RPN input mode to do unit conversions, matrix calculations, complex number calculations, vectors handling and function plotting. Find constants or formulas in the
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 CLN: Community Learning Network
Designed to help K12 teachers integrate technology into their classrooms. Includes over 225 menu pages with more than 4,200 annotated links to educational WWW sites, as well as over 100 WWW resources of their own.
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 Clocks and Curvature (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
The total curvature of any surface topologically equivalent to the sphere is 4 pi. This can be seen very simply from the definition of the curvature of a region in terms of the angle of rotation when the surface is rolled around on the plane; the only
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 Clocks  Bill Finzer, Key Curriculum Press
Two sketches illustrating useful Sketchpad animation techniques. Shows how to move the hour and minute hands at different rates, and how to convert the analog motion of the clock into digital switches.
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 Clockworks: From Sundials to the Atomic Second  Britannica.com
A site about the development of instruments that have measured time over the centuries. Each instrument has a page featuring a description and an illustrated diagram, and most include a QuickTime animation demonstrating how the mechanism works. Iinstruments
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 Clusters and Decagons  Ivars Peterson  Science News Online
A novel pattern made up of overlapping, 10sided tiles may serve as a model of how atoms arrange themselves into a quasicrystalline structure.
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 Clutch Hitting  Elan Fuld
Download the PDF of a study examining whether clutch (or choke) hitters exist in professional baseball. Using playbyplay data, Fuld found substantial evidence that clutch hitters exist in Major League Baseball, when sacrifice flies are considered as
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 Cmathématique  Téléfiction
Liens à consulter classés par sujet et par niveau; des problèmes du mois, un concours pour l'honneur dont les meilleures solutions de participants seront publiées sur le site; des capsules "crack" mathématiques offrant
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 CME Project  Center for Mathematics Education, Education Development Center, Inc. (EDC)
The CME Project is a fouryear, NSFfunded, comprehensive high school mathematics program that is problembased, studentcentered, and organized around the familiar themes of Algebra 1, Geometry, Algebra 2, and Precalculus. The CME Project sets as its
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 CMS  Science Fair Page (Cyberspace Middle School)  Dr. Larry Dennis; Department of Physics, Florida State University
A page for students who are using the World Wide Web to gather information on science fair projects. It includes: a help desk; practical hints for selecting and completing a project; descriptions of possible science fair projects; planning a class project;
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 Coastal Computer Company
An educational software company. Math titles, AlgebraMAKER and MathMAKER, drill students in basic skills, explaining the solution to each problem. Samples of these programs are available for download.
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 "The Code War"  Beyond Discovery  Dana Mackenzie et al.; National Academy of Sciences
An online science article from the Beyond Discovery series that explores the trail of developments in the branch of mathematics known as number theory that led to modernday encryption techniques. Contents include: Early Ciphers; The Enigma Challenge;
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 The Coffeecup Caustic  Roy Williams
You are drinking from a cylindrical cup in the sunshine. Sometimes, when the sun shines into the cup, you can see a crescent of light as the sunshine reflects from the inside of the cup onto the surface of the drink. This Java applet illustrates the optics
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 Coffee Hour Problem of the Week  Matthew McMullen
Classic and "found" problems, as well as original challenges, in number theory, logical reasoning, statistics, calculus, geometry, and algebra. McMullen has posted PDFs of the PoWs, as well as their solutions, since 2007.
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 Cognitive Apprenticeship (Learning and Mathematics)  Collins, et al.; Math Forum
In a chapter entitled "Cognitive apprenticeship: Teaching the crafts of reading, writing, and mathematics," in the 1989 book Knowing, learning, and instruction: Essays in honor of Robert Glaser, Allan Collins, of BBN Laboratories, and John Seely Brown
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 Coin Flipping  Ken White
A page that allows you to gather data on virtual coinflipping experiments. Includes access to data on past coin flipping and an article about coin flipping.
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 Coin Flipping  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about flipping coins, such as "What is the probability of getting two heads and four tails?" and "What is the probability of getting two heads on four flips of an unbiased coin?"
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 Coin Problems  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
Tony has 11 more nickels than quarters. How many coins does he have if the total value of his coins is $2.65?
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 Coins and a Balance Scale  Bennett Haselton
You have twelve coins and a balance scale. One of the coins does not weigh the same as the other eleven, but you don't know if the odd coin is heavier or lighter than the others. How can you determine, in three weighings, which coin is the odd coin?
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 Coins, Art, and Math in North Bay  Ivars Peterson (MathTrek)
North Bay's Nipissing University hosted the annual meeting of the Ontario
Association for Mathematics Education, which attracted about 650 math teachers. As one of the featured speakers, I presented a talk on randomness. My examples included slot machines,
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 Colección de Juegos de Ingenio del Club Mensa  Javier García Algarra
Esta colección recoge juegos de ingenio y problemas de matemática recreativa publicados en diversas revistas de Mensa, la asociación internacional para personas con un elevado cociente intelectual. En cada problema se hace referencia
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 Colégio de Gaia, Grupo de Matematica
Math resources in Portuguese: Galeria de Sketches  a gallery of JavaSketchpad and Geometer's Sketchpad problems and sketches including the Pythagorean theorem (o Teorema de Pitágoras), Vector Addition (Adicao de Vectores), cutting a cube/parallelepiped
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 Collaborative Learning Discussion Archive  Math Forum
A special project hosted by the Math Forum, this discussion concerned collaborative learning, its definition, its effects on teachers and students, administration and assessment issues, and materials and resources. The discussion began as email conversations,
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 Collaborative Learning  Mathematics Education at The Math Forum
A collection of links to collaborative and cooperative learning resources on the Web, including articles, discussions, and teaching techniques that emphasize collaboration.
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 Collaborative Mathematics  Jason Ermer
Videos for connecting "a worldwide community of mathematical problem solvers" and "cultivating a productive attitude toward challenging problems: one of creativity, resourcefulness, selfconfidence, and perseverance." Two and threeminutelong challenges
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 The Collage Theorem  Cut the Knot!, Alexander Bogomolny
To find an IFS whose attractor is "close to" or "looks like" a given set, one must endeavor to find a set of transformations  contraction mappings on a suitable set within which the given set lies  such that the union, or collage, of the images of the
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