 Dave's Geometric Pix Gallery  David Joyce; Dept. of Mathematics & Computer Science, Clark University
Mandelbrot and Julia sets, with a generation form and an Explorer on which you can point and click to get more refined images;
Newton Basins and a form to generate them; a page describing tiling the hyperbolic plane; some wallpaper groups; a gallery
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 Dave's Math Tables: Areas, Volumes, Surface Areas  David Manura
Formulas for and diagrams of: areas of polygons (square, rectangle, parallelogram, trapezoid, circle, ellipse, triangles); volumes of polyhedra (cube, rectangular prism, irregular prism, cylinder, pyramid, cone, sphere, ellipsoid); surface area (cube,
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 The David Mulhall Centre  David Mulhall
Site with resources and suggested treatments for people with Dyslexia, Dyscalcula, Dyspraxia and Attention Deficit Disorder. Extensive site, linking to The David Mulhall Centres in London and the UK.
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 Davitily Math Problem Generator  Nguyen, Ly; and Pardue, David
Create worksheets and tests, including options for multiple choice, printable versions, and answer keys. Click to insert preworded questions in basic math, algebra, and geometry, the parameters of which vary randomly. Requires JavaScript. Also available
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 Daylight Savings Time  Jim Loy
A short explanation of Daylight Savings Time in the United States.
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 Day Of The Week Of Any Date  Jim Loy
An explanation of how to figure the day of the week for any date, with some detailed shortcuts and some tables you might memorize.
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 Dear Marilyn, About Leap Years (Math Chat)  Frank Morgan, MAA Online
Your explanation [in Parade Magazine] of September 13, 1998 that we may need to skip a leap year EVERY FEW THOUSAND YEARS because the tropical year (about 365.2422 days) is a bit shorter than the average calendar year (365.2425 days) neglects CHANGES
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 Deberes matemáticas: Ejercicios y problemas de matemáticas resueltos paso a paso.  FORTEC, Formación y Tecnología S.L.
Herramientas didácticas específicas para la enseñanza y el aprendizaje de las matemáticas de la E.S.O. Ejercicios, problemas, exámenes, temarios, todos resueltos y explicados paso a paso. Por suscripción.
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 Decimal Coins of the UK  Tony Clayton
The change to decimal coinage: Decimalisation Day. DDay was February 15th 1971. On that day the United Kingdom changed from the centuries old tradition of using 12 pence to the shilling and 20 shillings to the pound to a new decimal 100 new
pence to
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 Decimal numbers (Middle School Math)  Homeworkhelp.com, Inc.
A lesson on decimals: What is a decimal number? Converting fractions to decimals, and decimals to fractions; Adding and subtracting decimal numbers; Multiplying decimal numbers; Dividing decimal numbers; Rounding.
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 Decimal Places on a Number Line  NASA Lewis Learning Technologies Project
Decimal places: On a number line, which of the following numbers would be the farthest to the right? 0.001, 0.0015, 0.00099, 0.0005. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 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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 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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 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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 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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 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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 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
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 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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 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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 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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 Designs with Circles  Suzanne Alejandre
A Math Forum Web Unit. Includes some background on circles in Islamic cultures, and an activity exploring the geometry involved in some circle designs.
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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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 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 Algebraic Thinking  Suzanne Alejandre
Teacher lesson plan and student kinesthetic activities on the Traffic Jam activity and applet, as originally published in the inaugural (Fall, 2002) issue of ONMath, an electronic journal of the National Council of Teachers of Mathematics (NCTM).
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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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 Diario Fractal  Today´s Fractal  Juan Pablo Braña
A site from Buenos Aires, in English and Spanish, with a different fractal art image every day and archived galleries of past images.
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 Dice and Valentine's Day Symmetries (Math Chat)  Frank Morgan; Christian Science Monitor
A dice challenge from S. H. Logue: The six faces of four dice have these numbers on them: A 1 1 5 5 5 5 B 4 4 4 4 4 4 C 3 3 3 3 7 7 D 2 2 2 6 6 6. You and your opponent each choose one die to use throughout the game. Each round you both roll, and the
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 Dictionary of Number Words  Intergalactic Power & Light
A dictionary of English language words, phrases, prefixes, suffixes, and
symbols that describe numbers. Cardinal Numbers, Ordinal Numbers, very large numbers, Noninteger Real Numbers, Numeric Ranges.
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 A Dictionary of Units  Cleave Books
A summary of units of measurement worldwide (current units and a few of historical interest); conversion factors to the SI (Systeme International); an outline of the SI; its basic defining standards and some of its derived units; all the SI prefixes
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 Didax Educational Resources
Didax publishes and distributes books, manipulatives, and software for math, reading, science, and art. The site offers free demo software, product descriptions, information requests, technical support, and current national educational standards. Didax
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 Did You Know? Applications of Statistics  Ian Gordon; University of Melbourne, Australia
Short stories about the application of statistics in different fields: Analysis of Gambling Strategies; Random surgical operations; TV phonein polls; Was it the orange juice?; Sunlight and skin cancer; Firefighters cause damage?!; What was the question
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 Digital Deletions  Pierre Ysewijn
An interactive JavaScript version of Conway's Digital Deletions game, in which numbers in a string are lowered to zero or erased. Users can play with different numbers of digits, different strategy levels, different starters, different sources of digits
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 Digital Generation Unit Conversions  Digital Generation
Choose from 26 different categories of engineering and scientific units. Also available at http://www.webcom.com/legacysy/convert2/convert2.html and http://www.legacysy.com/~legacysy/convert2/convert2.html.
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 DigitalLesson.com  Mark Tully
Website for middle school math teachers that has middle school math lessons, games, projects and activities for use in the classroom. Free newsletter, other resources for sale.
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 DigitalLesson.com: Middle School Math Downloads  Mark Tully
Free printable math games, a free PowerPoint Mathegories game, and a free newsletter for middle school math teachers five times per school year. DigitalLesson.com also offers downloads of middle school math lessons, projects, and games at reasonable
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 Digital Library: Science, Mathematics, Engineering and Technology Education (SMETE)  NEEDS
This site contains a searchable working prototype of a National Science, Mathematics, Engineering, and Technology Education Digital Library; a prototype federated search for the math community and the American Mathematics Metadata Task Force (AMMTF);
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 Digital Library  The Exploratorium, San Francisco
The Exploratorium AtoZ. Archived webcasts, web cams, past exhibitions: stills, movies, sounds, and other experimental items. Online versions of a few of the Exploratorium's interactive exhibits; the Exhibit CrossReference  an experimental database
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 Digital Mathematical Performance  Gadanidis, George; Borba, Marcelo; Hughes, Janette; et al.
Watch video, liveacted dramatic storyboards, and animations of how people "perform" mathematics: Flatland, "Help Me, Fermi," Should Parallel Lines Never Meet," "The Pleasure of Making 10" (linear equations), "The Waiter" (the missing dollar problem),
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