 Cracking a Medieval Code  Ivars Peterson (MathTrek)
The first printed book on cryptology was written by Johannes Trithemius (14621516), an abbot in Spanheim, Germany, who was one of the leading intellectuals of his day. Bearing the title Polygraphiae libri sex ("Six Books of Polygraphy"), it was published
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 Cracking Kepler's spherepacking problem  Ivars Peterson; Science News Online
The familiar piles of neatly stacked oranges at a supermarket represent a practical solution to the problem of packing spheres as tightly as possible. Thomas C. Hales proved that no other arrangement of identical spheres fills space more efficiently,
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 Cracking the Myth of Ball Control  Ivars Peterson (MathLand)
Ball control has become common practice in a number of sports. In basketball, for example, coaches often urge their teams to slow down a game at certain times or to control its tempo. In professional football, "time of possession" has become a statistic
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 Crackpot Index  John Baez
A fun site which outlines how you can tell if a new theory is really from a "crackpot."
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 The Crafoord Foundation
For the promotion of scientific training and research; and also the care, upbringing and education of children and young people. Apply for scientific research grants, and see grant awardees. The Royal Swedish Academy of Sciences awards a Crafoord Prize,
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 Crafty Puzzles  James Cole, The Crafty Puzzles Company
A U.K. establishment selling wooden puzzles of all sorts: jigsaw puzzles, puzzle boxes, brain teasers, models, and functional pieces.
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 Cram Central: Advanced Placement Exam Prep  Apex Publishing
An online environment for AP review, with preparation tools and connections to AP students around the country. Free registration; strategies, resources, and study tips for students; strategies, resources, and a teachers' forum. Course outlines and online
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 A Craps Tutorial  Odds, Probability, and House Edge  Gayle Tellis
Intended to help students and teachers of math learn how to convert odds to probability (and viceversa) and to compute house edge of simple games such as craps and roulette. Includes a section on the rules as well.
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 A Crash Course in Symbolic Logic  D.J. Brasier; Math Forum, Ask Dr. Math FAQ
Is symbolic logic so hard that some people will just never be able to get it? In a gentle introduction to the notation and rules of derivation used in symbolic logic, Dr. Achilles shows why the answer to that question is 'No'.
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 A Crash Course in the Mathematics of Infinite Sets  Peter Suber; Philosophy Department, Earlham College
An introductory guide for philosophers, explaining the use of infinitary set theory.
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 Crashing Waves, Awesome Explosions, Turbulent Smoke and Beyond: Applied Mathematics and Scientific Computing in the Visual Effects Industry [PDF document]  Aleka McAdams, Stanley Osher, and Joseph Teran
The May 2010 issue of the Notices of the American Mathematical Society includes a PDF article (1.3M) entitled "Crashing Waves, Awesome Explosions, Turbulent Smoke, and Beyond: Applied Mathematics and Scientific Computing in the Visual Effects Industry."
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 Crazy Math Teacher Lady  Lisa Bejarano
A high school math teacher in Colorado, Bejarano began blogging after "an awesome 3 day experience at NCTM Denver." Original classroom materials by herself and her students regularly enrich her posts, which date back to that April, 2013 annual meeting
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 CRC Press LLC
A scientific and technical publisher of books, journals, regulatory newsletters, and environmental seminars. A searchable online catalog may also be browsed by topic, among others Engineering, Computer Science, and Math & Statistics.
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 Create 2D and 3D gnuplot Graphs
Input a function, vary parameters, plot 2D, 3D Surface, or 3D Contour, vary range displayed, and plot multiple functions at once. With help on various features, and links to graphing animated plots and varying the parameters. Part of the Shodor Educational
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 Create a Graph  National Center for Education Statistics (NCES)
Create your own graphs online: bar graphs, line graphs, area graphs, pie charts, or XY graphs (line, bubble, or scatter plots from Cartesian coordinates). Enter your own data, choose your own labels, preview your work, then print or save your graphs.
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 Creating an Active Learning Environment: Preparing PreService Teachers  Professor Hubert J. Ludwig; Math Forum
A page created at the request of Professor Hubert J. Ludwig, who organized a session on preparing preservice teachers to create active learning environments at the Annual Meeting of the Mathematical Association of America in Orlando, January 1013, 1996.
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 Creating NCubes  Dennis Clark
Web and PowerPoint files for learning how to make tesseracts, draw nspace cubes, and chase snakes, or certain closed paths (loops), in nspace cubes. Also, download Ncubes.exe, a Visual Basic program to draw Ncubes.
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 A Creative Encounter of the Numerical Kind: A Webquest for Middle Grades Math Students  Alice Gabbard
Students create their own numerals and base four number system for an alien civilization. This web quest features background and evaluation materials, links to state and national standards, and tips for teachers.
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 Creative Geometry  Cathleen V. Sanders
Teachers and students will find creative and interesting "handson" projects for most topics in the geometry curriculum. Each project is designed to help students understand, remember, and find value in the concepts of geometry. The pages are organized
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 Creative Java Puzzles  J. L. Read, Enchanted Mind
Games "good for exercising both sides of the brain." Knight's Tour: pass all the squares of the board with the knight, making only legal moves. Peg Solitaire: Remove all the pegs in the least amount of time, finishing with only one peg in the target hole.
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 Creative Problem Solving  Rob Eastaway
Eastaway's "portfolio" of interests includes short descriptions of his school talks, newspaper articles, and books he has authored or coauthored, such as Maths for Mums and Dads, The Hidden Mathematics of Sport, How to Remember Almost Everything, Ever,
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 Crewton Ramone's Blog of Math  Crewton Ramone
Ramone's blog, which dates back to July, 2009, has included posts  many with video  such as "Fractions Despite SPED," "Why Invert and Multiply," "4 Year Old Math Enrichment," "Fractions and Addends," "Fractions and Autism Do in Fact Mix," and "Fraction
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 Critical Evaluation Information  Kathy Schrock's Guide for Educators, Discovery School
With the advent of the World Wide Web and the huge amount of information it contains, students need to be able to evaluate a Web page for authenticity, applicability, authorship, bias, and usability. To help teachers get students started with this process,
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 Critical Issues in Mathematics (NCREL)  Pathways to School Improvement
Articles from the North Central Regional Educational Laboratory (NCREL). The Significance of the NCTM Standards; Ensuring Equity and Excellence in Mathematics; Locating, Using, and Integrating InternetBased Mathematics Materials; Providing HandsOn,
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 Critical Thinking Books and Software
Critical thinking books and software for home and classroom for use in mathematics, science, language arts, social studies, and more. Search for Content Area Mathematics from the classroom catalog or the home catalog.
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 Critical Thinking Puzzles  Eldhose
Puzzles, logical thinking riddles, word problems in blog format. Comment with your solution and read others' workings.
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 Critic of Technology in Schools Faces Tough Audience  Pamela Mendels
From the New York Times column on Education, an April 1998 report on public opinion of the views of Todd Oppenheimer (author of "The Computer Delusion", which apperared in the Atlantic Monthly magazine), from a public meeting concerning technology in
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 Crop circles: Theorems in wheat fields  Ivars Peterson  Science News Online
Patterns of circles and triangles surreptitiously flattened into the crops of southern England reveal the perpetrators' sophisticated knowledge of Euclidean geometry.
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 CrossAge Tutoring  Marah Fortson; Math Forum
An annotated bibliography: articles to help teachers deal with a classroom of learners with different abilities, different strengths and weaknesses, who are at different levels academically, behaviorally, and socially. The task of the teacher is a challenge,
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 Crossnumber puzzle (figure logic)  Alfredo Baratta
Cross figure puzzles to print or play online. Also known as figure logic puzzles, cross figure puzzles resemble crosswords in structure, but with entries consisting of numbers rather than words, and clues based on math questions, e.g., "1 Across: The
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 Cross Number Puzzles  Rainer Typke
Cross number puzzles to solve online; log in to create your own. Also known as crossfigure, figure logic, or numberlock puzzles, cross number puzzles require numbers instead of words to complete a crosswordlike grid.
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 Crossroads in Mathematics: Standards for Introductory College Mathematics Before Calculus  American Mathematical Association of TwoYear Colleges (AMATYC)
A searchable book on the Web that addresses the need to establish standards for the mathematics programs that bridge the gap between high school mathematics and college calculus. It also aims to satisfy the needs of students who do not plan to study calculus.
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 CRUME'S First Volume  What Will Mathematicians Think?  Research Sampler: John and Annie Selden, Eds.
A description of the first volume of Research in Collegiate Mathematics Education, first in a series of annual volumes (CMBS Issues in Mathematics Education, Vol. 4, 1994), in Undergraduate Mathematics Education Trends, January 1995.
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 CRUX Mathematicorum with Mathematical Mayhem  Canadian Mathematical Society
The Digital Supplement to the Canadian Mathematical Society's Problem Solving Journal, for those who practice or teach mathematics. Published eight times per year, the materials at this site are available to all subscribers of CRUX; a sample issue is
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 Cryptarithmetic Puzzle Solver  Naoyuki Tamura
Enter a cryptarithm or select an example, such as SEND + MORE = MONEY. Also, puzzle generators based on themes such as color names, fruits, vegetables, and numeral words in English, French, German, Spanish, and Italian.
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 Cryptarithms  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Cryptarithms are brain teasers obtained when digits in numerical calculations have been replaced by letters. Customarily, distinct letters stand for different digits. Another term, Alphametics, denotes cryptarithms in which letters form meaningful words,
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 Cryptarithms Online  Jorge Soares
Mathematical puzzles in which the digits are replaced by letters of the alphabet or other symbols. Brainteasers by the author; cryptarithms from the journal Sphinx; a primer; books on cryptarithms, and links to relevant sites on the Web.
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 Cryptoclub  Vera Pless, Janet Beissinger
This website includes tools to encrypt and decrypt messages, an
animated treasure hunt, a classroom message board to send and
receive encrypted messages, and a place to explore mathematics
topics related to cryptography, such as prime numbers and
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 The Crypto Drop Box of the American Cryptogram Association  Jerry Metzger
The American Cryptogram Association (ACA) is a nonprofit volunteer organization devoted to disseminating cryptographic knowledge. Members make up and solve their own creations strictly for the fun of it. Every two months, the ACA journal, The Cryptogram,
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 A Cryptographic Compendium  John Savard
A book about cryptography with information about a large number of cipher systems and a limited coverage of cryptanalysis. It is mostly concerned with the various kinds of ciphers people have used and only mentions a few things about breaking ciphers.
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 Cryptography AZ  SSH Communications Security
An introduction to the basics of cryptography: Basic Terminology; Basic Cryptographic Algorithms; Digital Signatures; Cryptographic Hash Functions; Cryptographic Random Number Generators; Strength of Cryptographic Algorithms; Cryptanalysis and Attacks
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 Cryptography  Corey Reed
An introduction to cryptography, in particular affine enciphering applied to the alphabet, focusing on the use of linear algebra. Includes a primer on bases and modulus algebra and extensions for deciphering an affine enciphered message, using keys to
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 Cryptography World  The Cryptography Introduction
An introduction to cryptography and cryptoanalysis. Includes space for a repository of papers on the subject; introductory text; cryptography news through Google; and links to providers.
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 Cryptonomicon.Net  Matthew S. Hamrick; PhPNuke
A community portal site for amateurs and professionals with an interest in cryptography. The site has some original content and news stories, but the Web links section (with over 1100 links to crypto and security related sites) is most interesting.
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 Crystallographic Topology  Johnson, Burnett, Oak Ridge National Laboratory
The Topology of Crystallographic Groups and Simple Crystal Structures. A tutorial on some applications of Geometric Topology to Crystallography. The topology of crystallographic groups is approached using orbifolds, and that of simple crystal structures
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 CrystalMaker
A Macintosh program to display and manipulate all kinds of crystal structures. Using the free companion program, CrystalDiffract, CrystalMaker files can be used to generate xray and neutron powder diffraction patterns. Main features: In "PhotoColour"
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 Crystals: Crystallography & Systems  Suzanne Alejandre
A Math Forum Web Unit. Students studying polyhedra enjoy seeing the structures as they occur in the real world. Crystalline structures can be categorized into seven crystal systems: see photographs of beautiful crystals or make paper models of crystals
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 CS22: Discrete Math  Brown University
An introduction to discrete math with a focus on proof, logic, proof by induction, cryptography and networks of processors: lessons, homework, solutions, and information. "Discrete mathematics" refers to the distinction between discrete sets (for example,
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 CS Bits & Bytes  The National Science Foundation
CS Bits & Bytes highlights innovative computer science research, often at the intersection with other disciplines, and includes profiles of the individuals in the field, links for further exploration, and interactive activities. Past issues of the
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 C++ Simulator of a Post Machine  Alex Vinokur
The program simulates Deterministic and Nondeterministic Multitape Post Machine. The following demo Post machines are demonstrated with using the C++ Simulator: an addition of one to a number (Deterministic, 1 tape), an addition of two numbers (Deterministic,
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