 Decision Development Corporation
Software for K12 students and teachers, for all platforms. Math software included separately and as part of other product lines. (Gigamath Playground and Junior Gigamath Playground offer word problem practice for ages 714 and 48 respectively; Ellen
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 Decision Making Information  Model Education Systems Associates: MESA, Inc.
MESA specializes in the development, implementation and use of decision support systems and related quantitative information resources, especially quantitative tools for research, evaluation and policy analysis directed toward children and their living
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 Decision Theory and Decision Trees  Mind Tools
A method for organizing and analyzing financial decisions, and other decisions with clear numerical payoff.
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 Deckulator  Michael B. Moore
For your collectible trading card games, especially Magic: the Gathering. Deckulator calculates the percentage that a card combination will occur in the first cards dealt off the top of the deck. The calculator uses multivariate hypergeometric distribution.
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 Deep in the Jungles  Ivars Peterson (MathTrek)
Humans are predisposed to seeing order and meaning in a world that too often presents random choices and chaotic evidence. Random events sometimes get linked into a meaningful, though ultimately bogus, scenario... At the same time, the mathematics of
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 Deepwater Horizon Incident  The National Oceanic and Atmospheric Administration (NOAA)
NOAA has put together a site full of resources about the Deepwater Horizon oil spill in the Gulf of Mexico. In the left margin, choose "Information for: Students and Teachers" to access data sets as well as articles for the classroom, such as a Q&A that
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 Defending the Roman Empire  Ivars Peterson (MathTrek)
Questions of military strategy can be handled mathematically. Charles S. ReVelle of Johns Hopkins University in Baltimore and Kenneth E. Rosing, recently retired from Erasmus University Rotterdam, describe their approach in the AugustSeptember American
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 Defining Geometric Formulas (Ask Dr. Math FAQ)  Math Forum
Definitions of two and threedimensional figures in general, and a note on dimensions.
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 The Definitive Four Fours Answer Key  David A. Wheeler
From 0 up to 40,000, whole number mathematical expressions that use only common mathematical symbols and exactly four 4s. Wheeler offers his solutions in three different formats: an abbreviated list of answers; a text file of results, mathematical expressions,
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 Dekov Software
Educational software, a journal of computergenerated Euclidean geometry, and a computergenerated encyclopedia of Euclidean geometry. Current software titles include: Solving Triangles (stepbystep solutions to triangle problems in elementary geometry);
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 Delaware State Data Center  Delaware Economic Development Office
A focal point for the distribution of census information in Delaware and for the dissemination of other information from the federal government, state government and other sources, coordinating the use of census and other data for economic development.
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 Deliberative Discourse Idealized and Realized: Accountable Talk in the Classroom and in Civic Life  Sarah Michaels, Catherine O’Connor, Lauren B. Resnick
An article in PDF format. Abstract: Classroom discussion practices that can lead to reasoned participation by all students are presented and described by the authors. Their research emphasizes the careful orchestration of talk and tasks in academic learning.
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 Delphi For Fun  Gary Darby; Intellitech Systems Inc.
Delphi is based on the Pascal programming language developed in the early 1970s by Niklaus Wirth and named after mathematician Blaise Pascal. This site explores the use of programming as a tool in math problem solving, discussing interesting problems,
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 Delta Blocks  Hop David
A way to model different 3D tessellations and a tool for studying geometry, crystallography, and polyhedra. Delta blocks were inspired by M. C. Escher's print "Flatworms," which he said demonstrates that one can build a house not only with the usual
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 Demiregular Tessellations  Totally Tessellated
Color renditions and a real example of a demiregular tessellation. Templates allow you to print renditions of each tessellation suitable for coloring activities.
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 De Moivre's Theorem  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about de Moivre's theorem, including its usefulness and proofs.
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 The De Morgan Journal  London Mathematical Society
The De Morgan Journal aims "to encourage academic mathematicians to reflect on current issues in mathematics education at all levels, from primary school to graduate studies; to encourage them to explore links between higher mathematics and elementary
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 Demos with Positive Impact  David R. Hill and Lila F. Roberts
Demos with Positive Impact organizes effective math teaching tools. Submit your own demo, or browse the existing collection of physical demos, calculator demos, databased demos, browserbased demos, and software demos, each with statements of objectives,
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 Demos with Positive Impact  David R. Hill and Lila F. Roberts
A collection of classroom demonstrations that use some form of instructional technology. The authors invite others to submit demos and provide them with feedback on the demos already collected. Demos are organized under the levels of Pre Calculus, Calculus
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 Department of Mathematics and Computer Science  North Carolina School of Science and Mathematics (NCSSM)
Learning materials for teachers and students include resources on algebra, advanced functions, and mathematical modeling; data sets used with the NCSSM textbook Contemporary Precalculus Through Applications; the AP Calculus Web Center; and Mathematics
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 Department of Science & Mathematics Education: Research and Development  Univ. of Melbourne, Australia
Read faculty research and learn about their projects and interests: children's understanding of statistical and probabilistic concepts; the negotiation of meaning in mathematics & science classrooms (The Classroom Project); the expression of algorithms
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 Derek's Daily Math  Derek Orr
"Every Number Has a Story to Tell." This blog by an undergraduate at the University of Pittsburgh details number theoretic properties for every day of the calendar year. Orr, a physics and math major, also maintains a list of "Interesting Propositions/Theorems
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 Derivative and Integral  Bill Finzer, Key Curriculum Press
Two sketches demonstrating elementary calculus concepts. Each sketch shows the graph of a function and the graph of its derivative. One sketch lets you change the graph of the function and watch the effect on its derivative. The other sketch lets you
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 Derivative Calculator  David Scherfgen
Compute derivatives of functions online, for free. Supporting symbolic computation of the 1st, 2nd, and subsequent derivatives of multivariable functions, the Derivative Calculator dynamically typesets expressions while you type them. derivativecalculator.net
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 Derivative  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about derivatives, from definitions and explanations to alternate forms of the derivative formula.
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 The Derivative Project: Using Appropriate Technology to Teach the Concept of Derivative Via a Graphical Approach  Lisa Denise Murphy
Murphy has developed an instructional unit that uses a motion sensor and related software to introduce the concept of a derivative, and tested it in a firstsemester calculus class, with very good results. She is now engaged in expanding this project
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 Derive  Texas Instruments, Inc.
DERIVE software is a Computer Algebra System (CAS) for personal computers (Windows, DOS). In addition, the CAS technology in DERIVE is incorporated in TI89 and TI92 calculators. Derive applies the rules of algebra, trigonometry, calculus, and matrix
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 Desafios Matemáticos  Paulo Ferro
Cinco desafios novos cada mês. Ferro, um professor de matemática licenciado pela Universidade de Coimbra, tambem oferece demonstracões de geometria dinâmica, jogos matemáticos, biografias de matemáticos, exames
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 Descartes 3  Ministry of Education, Culture, and Sport, Spain
Create interactive math lessons in web page format with this applet, or download any of more than 60 already created applets (ranging from "representing numbers on a straight line" to "tables and algebraic terms," from "geometry and a game of billiards"
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 Descartes' Formula (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
The angle defect at a vertex of a polygon was defined to be the amount by which the sum of the angles at the corners of the faces at that vertex falls short of and the total angle defect of the polyhedron was defined to be what one got when one added
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 Descartes' Rule of Signs  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A discussion by Scott Brodie of the basis of the attribution to Descartes of the proposition now known as Descartes' Rule of Signs: The number of positive roots of a polynomial with real coefficients is equal to the number of "changes of sign" in the
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 Description of the Julia sets of the Cauliflower fractal  Frans Faase
Investigation of the Julia sets of the Cauliflower fractal, which is a fractal generated by two linear translations with three parameters. The generated fractal can either be solid, connected, or disconnected. The author shows that two Julia sets consisting
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 Descriptive Geometry  Petr Plavjaník
Software for creating and printing drawings, including conic sections, color fillings in Monge's projection, and axonometry. In English and Czech.
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 Design Ideas  Julie Coghill
A series of articles that discuss quilt design using proportion, asymmetry, and Pythagorean triples.
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 Designing a Sustainable Standardsbased Assessment System  Don Burger; Midcontinent Regional Educational Laboratory (McREL)
Designing and implementing a sustainable standardsbased system that consistently yields high student achievement involves more than setting and measuring academic goals. Changing to a standardsbased system provides an
opportunity to reexamine the
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 Designing Effective Professional Development: Lessons from the Eisenhower Program  U.S. Department of Education
The second report of the National Evaluation of the Eisenhower Professional Development Program, Part B (State and Local Activities), a multiyear evaluation being conducted by the American Institutes for Research (AIR) under a contract with the U.S.
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 Designing Geometric Figures  Tim Fahey
Geometric constructions: instructions for constructing a variety of geometric shapes and patterns. Symbols, basic constructions, basic shapes, and how to design patterns.
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 Design Science  Design Science, Inc.
Math publishing and presentation tools for the web: MathType, the professional version of Equation Editor, for Windows or Mac; WebEQ, for building interactive math web pages; MathFlow, math publishing for the enterprise; and MathPlayer, to display MathML
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 Design Your Future  Math, Science, and Technology for Girls  Autodesk, Inc.
The Design Your Future mission is to provide practical, inspiring, hands
on opportunities for young women to become aware of, explore, and pursue
math, science, and technologybased careers. It provides a number of opportunities, including: a tool
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 Desmos  Desmos Inc
This free online graphing calculator zooms in and out of plots, offers slider bars to explore parameters, switches between Cartesian and polar coordinates, and more. Save sketches, mark points of interest, turn on "projector mode" for thicker, darker
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 Des Trucs et des Maths  Philippe Picart
Sur le nombre pi; le nombre d'or; le Rubik's cube; des ressources à télécharger; et "des trucs de maths divers," comme un JavaScript qui répond à la question "Quel jour de la semaine estu né?" Avec un coins des
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 Determinación Geométrica de los Números Primos y Perfectos  Omar E. Pol
Un breve ensayo en que "se describe la geometría que determina la distribución exacta de los números primos y también de los números perfectos. Se ilustra el texto con diagramas originales; se muestra el modelo principal
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 Detracking America's Schools: The Reform Without Cost?  Brewer, Rees, Argys; Phi Delta Kappan
The practice of grouping school students by level of ability, known as tracking, has long been used in American public schools. In recent years, opponents of tracking have argued that belowaverage students are hindered by being grouped together, while
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 DevApprentice: Software Developer Apprentice  Kent Griffin
An online resource for learning elementary computer programming. Write and execute real programs, including graphics, in your web browser. Includes a programming problem of the week, examples, instructions, a glossary, and the online programming environment.
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 developer.com's collection of math Java applets  EarthWeb, Inc.
A browsable, searchable collection of links, authors, notes, and details about Java applets contributed to developer.com. Software is organized into the categories of basics and children's, fractals, games and puzzles, general, geometry, plotting, graphing,
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 Developing A General 2nd Degree Diophantine Equation x^2 + p = 2^n  Thien Do; Westmoore High School, Oklahoma City, OK
Using methods of congruences, the author shows that if p = 3 there is only one positive solution (1,2), and if p is any other odd prime not congruent to 7 mod 8, there are no solutions. Introduction; Methodology; Conclusions; Further Works; Acknowledgements;
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 Developing Educational Standards for Schools  Charles Hill; Putnam Valley Schools, New York
An annotated list of sites that have educational standards documents prepared by various states and professional organizations. View standards by subject area or U.S. state. There is a list of state education departments, and resource pages on: U.S. government;
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 Developing Function Sense with SAQs  Judah Schwartz
A work in progress, this is an online book on the philosophy of teaching functions in middle and high school algebra. He has come to believe "that approaching algebra through the study of functions using symbolic and graphical representations simultaneously
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 De Viribus Quantitatis  The University of Bologna
Luca Pacioli, a Franciscan monk, mathematics tutor, and colleague of Leonardo Da Vinci, wrote this foundational text of modern magic and numerical puzzles between 1496 and 1508. De Viribus Quantitatis (On the Powers of Numbers) contains the first ever
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 Devising channels that nurture ingenuity and creativity in mathematics classes.  Helen Christensen; Loyola College; The Math Forum
Summary of a presentation given at the 1996 Joint Mathematics Meetings in Orlando, Florida. Original projects and individual journals can challenge students who are more linguistically oriented, and who crave expression for their ingenuity and creativity
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