 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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 Rincón Matemático  Mario Augusto Bunge
Revista electrónica de matemática básica. Temas de análisis, cálculo,
geometría, probabilidades. Problema del mes. Foros.
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 Rincón Matemático Tests interactivos  Mario A. Bunge
Exámenes multiple choice de Precálculo, Matemática, Análisis Matemático y
Álgebra lineal. Cada examen se presenta en dos formatos: PDF y HTML.
El PDF se imprime y se utiliza como una hoja de examen. Realizada la
prueba, se recurre al HTML (quiz
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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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 The Rise of Calculus  MacTutor Math History Archives
Linked essay describing the history of Calculus from the Greeks through Newton and Leibniz, with 28 references (books/articles).
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 Risorse Internet per la storia della matematica  Claudia Lamberti
Internet resources for mathematics, science, and engineering history selected from the University of Pisa Libraries.
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 Rite Item  Jim Preston
Software to download: ANYANGLE (Windows, DOS; a geometry solver that provides a method of finding answers to problems involving triangles, and offers scale views and supplementary data to back up the numerical results); and PARTYDOT (a program for creating
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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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 RJN's More Digits of Irrational Numbers Page  Nemiroff, Bonnell
All digits accessible here were computed by Robert Nemiroff and Jerry Bonnell. The Digit Warehouse: e, sqrts of 2, 3, 5, 6, 7, 8, 10 to millions of digits.
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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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 Rob Barry's Website
Recent stories by The Wall Street Journal investigative reporter who specializes in computerassisted reporting, which he describes as "the practice of wrestling large sets of data into compelling narratives." Barry's articles have ranged from insider
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 Robert Abbott's Mazes  Robert Abbott
Two very difficult puzzles programmed by Oriel Maxime and based on mazes in Abbott's books: the Sliding Door Maze, and Theseus and the Minotaur. Also a collection of reviews of the books SuperMazes and Mad Mazes, with more puzzles (but nothing interactive),
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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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 Robert's Online Applications  Robert Lum
Java applets to assist with financial investments: commissions pricer, derivatives pricer, loan pricer, option pricer, option strategy visualizer, portfolio pricer, quote sheet, stock volatility charts, and tax pricer (1999, 1998, 1997, 1996 or 1995).
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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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 Robotic Navigation with Constraints  J. A. Sethian
A paper and movie on robotic navigation. Finding the Shortest Path: The equation that describes the arrival time of this expanding front as it depends on the possible speed at any point and direction is the Eikonal equation. The fast marching method is
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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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 Rocky Mountain Mathematica  Ed Packel, Stan Wagon
Introductory and intermediate workshops on Mathematica for teachers of mathematics and other scientific subjects. Workshops are held in Colorado during early July. The site includes registration information, schedule, and syllabi.
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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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 The Role of Examples in Learning Mathematics  Annie and John Selden; Mathematical Association of America
"Examining examples and nonexamples can help students understand definitions.... Is the provision of examples always desirable? Would it perhaps be better to ask undergraduate students to provide their own examples and nonexamples? Would they be able
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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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 Rolf's Calculator  Rolf Howarth
A fully featured JavaScript scientific calculator that includes trig functions and logarithms, factorials, 12 levels of parentheses, logs to base 2, bitwise logical operators, hex, octal, binary and ascii display.
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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 Dice  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about rolling dice, cube and octahedral, fair and biased, once and many times.
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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 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 and decimals (Classics log)  John Durham
A letter to a Classics mailing list about the origin of and ease of calculation with Roman numerals.
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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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 The Roman Press, Inc.  Steven Roman
Home page of a California mathematics professor, including research articles, books and textbooks, and software.
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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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 The Roots of the Equation  James Cleveland
Blog by a high school algebra teacher in New York City "trying to figure out how it all fits together ... [and] creating interdisciplinary problems, projects, and thinking." A Math for America (MfA) fellow, Cleveland has blogged since June, 2011, with
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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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 Rossman/Chance Applet Collection  Franciso Garcia, Carlos Lima, and Beth Chance
Applets for simulating confidence intervals for population parameter, tintervals for different population shapes, behavior of regression line, histogram bin width, sampling Reeses Pieces, sampling 2002 U.S. Senators, sampling pennies, sampling words
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 ROSSMANCHANCE.COM  Allan J. Rossman & Beth L. Chance
Workshops and presentations, publications, and current projects by the authors of the Workshop Mathematics Project textbooks. See tables of contents, instructor guides, sample syllabi and exams, and answers to activities from books in the Workshop Statistics
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 The Ross Program  The Ohio State University
For high schoolers, the OSU Department of Mathematics offers an intensive summer experience designed to encourage motivated precollege students to explore mathematics. Over the course of eight weeks, students are immersed in a world of mathematical discovery.
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 Rotations (SMILE)  Susan Nash, Lake View High School
A lesson designed to teach students to define rotation as the composite of two reflections over intersecting lines; identify rotation images of a figure; and recognize and apply the properties of rotation. From the Graphs and Visuals section of a collection
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 Rough math: Focusing on rogue waves at sea  Ivars Peterson  Science News Online
Ocean currents and large fields of random eddies can focus a steady ocean swell to create unusually large waves. A current or eddy field acts like an optical lens to focus the wave action, says applied mathematician Bengt Fornberg of the University of
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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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