 The RightAngle Triangle Solver  Steve Ayers
Input two sides of a right triangle, or one of its sides and one of its angles, and this site calculates the remaining sidelengths and angles. Also, convert decimals and fractions, and imperial and metric units of measure. Requires JavaScript.
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 Right Brained Math  Brandon Price
"Searching for divergence and creativity in all that mathy stuff." Price teaches algebra, geometry, statistics, and robotics at Austin's Khabele School, an International Baccalaureate (IB) World School. His blog, which dates back to March, 2013, has
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 Rigol'Math: énigmes, problèmes et curiosités mathématiques  JeanMarc Deleuze
Le calcul de Pi; le Jeu de Nim; Convertisseur base 10 > base 2; Multiplier sur les doigts; Multiplication égyptienne; Le carré magique; TicTacToe; Coloriage; et beaucoup plus.
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 Rinus Roelofs
Geometric sculpture, animation, structures, and "rhinoceros" (knots) by Roelofs, who exhibited as part of the Escher Centennial celebrations. After studying Applied Mathematics at the Technical University of Enschede (Netherlands), Roelofs earned a degree
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 Rivendell Educational Archive  Leigh Denault
An educational archive of materials in botany, history, math, science, drama, literature, philosophy, and art. Math resources include mathematician biographies, a fractal image gallery, and a bibliography.
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 River Crossing (Math Exploration Quilt)  Rik Littlefield; Hanford School
You want to cross a river to reach a point exactly opposite where you are currently standing. Explore this problem stepbystep, encountering the following basic ideas: 1) Pythagorean theorem; 2) time = distance / speed; 3) distance = time * speed; 4)
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 Riverdeep  Mathematics  Riverdeep Interactive Learning Limited
Online resources for students, educators, and parents, that build on Riverdeep Interactive Learning's courseware and interactive simulations. Read about or demo Destination Math, a curriculum on CDROM in Basic Mathematics, PreAlgebra, and Algebra I
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 Road Sign Math  Jamie Thingelstad
"Driving + Math = Fun." A game to play on the road, identifying signs that suggest basic or advanced arithmetic, or that display constants, sequences, or primes. See digital photographs of actual street and highway signs that meet the "RSM" rules. Submit
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 Robert J. Lang Origami  Robert J. Lang
Lang has catalogued and diagrammed over 400 models, combining aspects of the Western school of mathematical origami design with the Eastern emphasis upon line and form. Read about origami mathematics, which mathematically describe the underlying laws
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 Robert Kaplinsky  Glenrock Consulting  Robert Kaplinsky
Lessons consist of "The Challenge(s)," "Question(s) To Ask," "Consider This," and alignments to Common Core State Standards (CCSS): "How Can We Water All Of The Grass?" and "How Much Money Should Dr. Evil Demand?" and "How Did They Make Ms. PacMan?"
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 Robo Compass
"Geometrical constructions made easy": type commands such as "draw segment AB between points A and B" and "construct an arc z with center O and radius which is length of segment y," then watch Robocompass draw the construction onscreen with its animated
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 Robotics: Sensing, Thinking, Acting  The Tech Museum of Innovation, San Jose, CA
An exibit designed to introduce the science behind the design and operation of robots. Features four exhibit areas: Universal Robots: History and Workings of Robotics; Machines and Man: Robotics and Ethics in the 21st Century; Robot Art: Four Bay Area
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 RockandRoll Bridge  Ivars Peterson (MathTrek)
Startling scenes of rippling pavement, featured in a classic film that captured the 1940 destruction of the Tacoma Narrows suspension bridge in Washington state, rank among the most dramatic and widely known images in science and engineering. This old
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 Rockin' the Standards
Musical recordings by a rock band led by a veteran elementary school teacher who takes the lyrics from common tunes and changes them to help kids remember what they've been taught in school. Each of the fourteen songs on the album "Rockin' the Standards
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 Rodney Carr's Home Page  Deakin University, Australia
Books and software on statistics and advanced spreadsheet design. Contact the author for passwords to access downloadable documents and executable Microsoft Excel workbooks such as XLStatistics, for statistical analysis of data; XLGenetics, for illustrating
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 The Role of Calculators in Math Education  Heidi Pomerantz, Bert Waits for USI/CPMSA
This PDF article outlines the benefits of calculator use in mathematics classrooms from kindergarten through the university level, describing how calculators, when used appropriately, can be a tool for learning mathematics. The document has six sections:
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 Roles of calculators in the classroom  Pedro Gómez and Bert Waits
The site contains the extended papers of the conferences presented in the Topic Group 18 of the International Congress of Mathematics Education held in Seville in July, 1996. Papers are presented both as web pages and as PDF files.
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 The Roles of Interest and Mathematical Beliefs in Preservice Teachers' Learning to Mentor Online [PDF]  Ray & Renninger
Paper presented as part of a symposium, American Educational Research Association, Chicago, IL. A study of preservice teachers working with the Math Forum's Online Mentoring Guide.
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 Rolling a Die Until Every Face Has Appeared (Math Chat)  Frank Morgan, MAA Online
How many times do you think you need to roll a normal die to be 90% sure that each of the six faces has appeared at least once? Why? Answer: It takes 23 rolls, as Al Zimmerman discovered in a computer experiment rolling 5000 dice until 90% of them had
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 Rolling and Learning® with trisquare dice  Creative Enterprises, Inc.
A book describing math games to be played with 14sided dice, suitable for grades K6 or 8. Order form available on the web.
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 Rolling with Reuleaux  Ivars Peterson (MathLand)
Why is the cover of a manhole round? The usual answer is that a circular lid, unlike a square or hexagonal cover, won't fall through the opening. The circle works because it has a constant width, defined as the distance between a pair of parallel lines
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 Rolocu: the Colour Twist Puzzle  Charles Edge
Use logic and planning to put the pieces into place so that all rows and columns have all the colours in them.
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 A Romance With Numbers  K. Venkatasubramanian
Biographical information and thoughts about Srinivasa Ramanujan, from The Hindu, December 24, 1993.
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 Roman Numeral Conversion  InnoVision Technologies
Enter the Arabic number you want to convert to Roman, as long as it's less than 4000.
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 Roman Numeral Date Conversion Guide  Christopher Handy
A guide to deciphering Roman numeral year dates as commonly found in both modern and early printed books, including a Java applet that accepts Roman numeral input in the range 14,999 and converts it to Arabic form. The page explains the basic principles
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 Roman Numerals 101  Oliver Lawrence
The Romans used only seven letters; the combination of a letter and its position could represent any number. They also used a line above the letter, so the numbering system actually represents our own very closely, with fourteen different symbols. The
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 Roman Numerals and Dates  Paul Lewis
An illustrated introduction to Roman numerals, including Roman dates and calendar conversion, history and uses, a page on The Great 1999 Question, and a quiz. Three conversion tables are provided: Numerical 11449; Numerical 14502100; and Alphabetical
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 Roman Numerals Defined  Jim Loy
A listing of some common Roman numerals and a short explanation of how they work.
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 Roman Numerals  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about Roman numerals, such as how they represented decimals and fractions; with memory aids for remembering what letter represents what value.
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 Roman Numerals  Math Forum, Ask Dr. Math FAQ
Basics: How do I read and write Roman numerals? What are the rules for subtracting letters? How do I write large numbers? Web resources: introductions, charts, calculators, and converters. Calculations: Did the Romans use fractions?
How can I use Roman
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 Ron Blond  Ron Blond
Circle geometry applets to explore inscribed and central angles, tangents and radii, and tangents and inscribed angles. Also, applets illustrating the quadratic function (completed square and the discriminant), transformations of the sine and cosine functions,
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 Rose and Twinkleberry's Guide to Building Your Own Puzzles Using LEGO Building Blocks  Doug Walker
Plans for making 32 classic puzzles using LEGO blocks.
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 Rosebush Math Line Puzzles  Math Forum
Three puzzles: 1) plant 7 rosebushes so that they form 6 straight lines with 3 rosebushes in each line. 2) plant 10 rosebushes in 5 straight lines with 4 bushes in each line. 3) plant 19 rosebushes in 9 straight lines with 5 bushes in each line. Questions,
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 Rounding a Decimal  NASA Lewis Learning Technologies Project
Round 12.5861 to the nearest hundredth. A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Rounding Down?  Jim Loy
This is an article about the difference between rounding and truncation, with some stories about the effects of rounding (or truncation) on computer programs.
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 Rounding Numbers  Math Forum, Ask Dr. Math FAQ
How do you round a number to the nearest tenth (10th), hundredth (100th), thousandth (1000th), etc.?
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 Rounding Seconds  NASA Lewis Learning Technologies Project
Erv ran the 110 meter high hurdles in 13.27 seconds. His teammate, Willie, ran the same race in 12.91 seconds. Rounded to the nearest tenth of a second, how much faster was Willie's time? A detailed answer is provided. From NASA's 9th Grade Math Proficiency
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 Route ICS (formerly DeweyWeb): Interactive Communications and Simulations  Univ. of Michigan
An effort to link distant schools and expand the classroom experience: using telecommunications and computer conferencing, students can spend part of every school day in a "global classroom." Crossroads: The Route 12 Project is a grassroots attempt to
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 Roxanne Eckenrode's Storefront  Lulu.com  Free SelfPublishing  Roxanne Eckenrode
Selfpublished math worksheets. Several are free. They are downloadable and printable; correct answers will spell out a message or fill in a puzzle.
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 Royal Tyrrell Museum of Palaeontology
Virtual site for a science museum named for Joseph Tyrrell, who in 1884 travelled to what is now Alberta, Canada to study coal deposits and found the first dinosaur remains ("Albertosaurus") in the Drumheller area. The museum's mandate is to collect,
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 R. S. Schaeffer  Randy S. Schaeffer, Math & Computer Science, Kutztown University of Pennsylvania
Schaeffer teaches a course called "Methods of Teaching Secondary Mathematics." Download the lessons created by his students that call on Geometer's Sketchpad, graphing calculators, and Microsoft Excel. Lesson topics address parallel lines, box and whisker
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 RU4Math
Games and events for elementaryaged students from Pulaski and Montgomery counties, and Radford City schools, who participated in the RU4Math Fest of March 22, 2003, held at Radford University. Shockwave games about logic and simple equations, currency
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 Rubik's Cube Information  Michael Reid
All about Rubik's Cube  even a mailing list. Site contents include: the Nederlandse Kubus Club; Rubik's cube pages on the Web; Cube books; Sources of cubelike puzzles; the author's notes, including an optimal cube solver; other Cube solutions on the
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 Rubik's Games  Androsoft
Dedicated to the first PC CDROM game from Erno Rubik, Rubik's Games contains 5 subgames: Rubik's Classic, Cover Up, Paint War, Rubik's Playground and ZigThrough. Download the Rubik's Games Web Site Plugin plugin or a demo of the Rubik's Game CDROM.
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 Rubik's Online  Rubik/Seven Towns
The official online site for the Rubik's cube. Play with the cube and other Rubik's games and puzzles online; find information on where to buy Rubik's products; use the forum to exchange views, opinions, comments, suggestions and anecdotes related to
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 Rubix Corner  Duane Cash
The site includes information regarding the Duane Cash Cube Collection now featured at Hessport's Rubikshop in their "collectibles" section. New puzzles include the Rubik's Triamese, Fusion, Fusion+, SpeedFusion, 5x3, and 4x3 Cubes, which give those interested
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 Rudi Mathematici  Rudy d'Alembert, Alice Riddle, and Piotr R. Silverbrahms
Matematica, giochi matematici, problemi, indovinelli e farneticazioni. Soprattutto una rivista, RM contiene Il Compleanno, Problemi del Mese, Bungee Jumpers, Soluzioni e Note, Quick & Dirty, Pagina 46, Paraphernalia Mathematica, Allegati ed Eventuali,
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 Russian Peasant Multiplication  Math Forum, Ask Dr. Math FAQ
What is Russian peasant multiplication? How do I use it? Why does it work? How is the Russian peasant algorithm connected to binary numbers?
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 Russian School of Mathematics
An afterschool math enrichment program "based on the best practices of advanced math schools in Russia and Europe and adapted to the US educational environment." Cofounded in 1997 by Inessa Rifkin and Irina Khavinson — who recall that, in the
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 Sabermetrics  The Baseball Archive
"The search for objective knowledge about baseball." Read a primer of Bill James' findings, or David Grabiner's manifesto on Sabermetrics. Studies address minor league equivalencies ("Are minor league stats a good precictor of major league performance?"),
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