 The Angle Defect of a Polyhedron (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
The angle defect at a vertex of a polygon is defined to be 2 pi minus the sum of the angles at the corners of the faces at that vertex. What is the angle sum for a polygon (in the plane) with n sides? Determine the total angle defect for each of the 5
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 Angles and angle terms  Mark Motyka, Math League Multimedia
Definitions and illustrations: What is an angle?; Degrees: measuring angles; Acute angles; Obtuse angles; Right angles; Complementary angles; Supplementary angles; Vertical angles; Alternate interior angles; Alternate exterior angles; Corresponding angles;
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 Angles of Reflection  John Benson and P. J. Karafiol
A backandforth intergenerational blog on math education, begun in January, 2011, by two Presidential Awardees in Mathematics from the state of Illinois.
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 AngryMath  Daniel R. Collins
Blog by an adjunct math lecturer at Kingsborough Community College who believes that "Math is a battle. It is a battle that feels like it must be fought ...," and for whom "math isn't beautiful or fun, but it is powerful, and that's what we need from
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 Animals & Art  M. Crook
A gallery of fractal images created using Ultra Fractal.
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 Animated Math Glossary  Math Advantage  Harcourt Brace School Publishers
A K8 glossary of common mathematical terms, categorized by grade. Each entry has an example, most of which are animated. An "other" section at the end of the alphabet gives tables of metric and customary measurements, time, formulas, and symbols. You
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 Animated Proof of the Pythagorean Theorem  Mark D. Meyerson; Mathematics Dept., U.S. Naval Academy
Starting with a right triangle and squares on each side, the middle size square is cut into congruent quadrilaterals (the cuts through the center and parallel to the sides of the biggest square). Then the quadrilaterals are hinged and rotated and shifted
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 Annenberg Institute for School Reform (AISR)  Brown University
The Annenberg Institute develops, shares and acts on knowledge that improves outcomes of schooling in America, especially in urban communities and in schools serving disadvantaged children. Institute Projects: Rethinking Accountability; Building Capacity;
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 Annie's Sketchpad Activities  Annie Fetter
Handouts for activities that incorporate JavaSketchpad, including: making a presentation sketch; investigating the properties of quadrilaterals; the Euler segment; morphing a simple figure to a circle; Napoleon's theorem; drawing a box and its net; and
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 Annual Pi Day  The Exploratorium, San Francisco, CA
"Founded by the the Exploratorium's own Prince of Pi, physicist Larry Shaw, Pi Day has become an international holiday, celebrated live and online all around the world." Read a brief history of pi; find activities for cutting π and wearing π; and
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 Answer Ace  MathSupport Co.
A Windows 95/98/NT math problem solver that helps students learn or review arithmetic, prealgebra, and basic algebra skills. Students enter specific problems and the software provides answers along with stepbystep help. A free trial is available for
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 Ant Math (MatheMUSEments!)  Ivars Peterson (Math Muse for Kids)
Imagine stepping into a pitchblack room. How might you figure out the room's size in the dark? You could, for example, carefully follow the walls and count how many steps you took going from one corner to the next all the way around. That would give
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 Apex Learning  Apex Learning
Standardsbased online curriculum for secondary education in the core academic subjects and Advanced Placement, available in multiple formats or packages to address differing purposes and populations: enrichment, credit recovery and remediation, virtual
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 APlusStudent Online Learning
Interactive math lessons with graphics, animation, and audio, based on Micromedia Flash technology. Teacherdesigned, standardsbased lessons. Parents can monitor the progress of their children. There is also homework help and an online gallery where
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 Apogee Tutors  Vimal Patel
Danbury, CT based tutoring services. We provide oneonone tutoring, group tutoring for middle school through college students.
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 Appetizers and Lessons for Math and Reason  Alan Selby
Logic Appetizers to test or or improve reading, writing and thinking skills, with definitions, concepts and proofs in many subjects (Chains of Reason; One or TwoWay Implications; Islands & Divisions of Knowledge; Deception); Advice (How to Study
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 Applications and Misapplications of Cognitive Psychology to Math Education  Anderson, Reder, Simon
A critical view of constructivism by three leading cognitive psychologists at Carnegie Mellon University. Decomposition and decontextualization; situated learning; constructivism; recommendations for research and instruction; overall conclusions; references.
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 Aquí Matemàtiques (Catalán)  Carlos Romero
Web and interactive materials in Catalán designed to facilitate and improve teacher training in mathematics. Goals: to provide curricular incentives for integrating technology into primary and secondary level teaching; facilitate access to curricula;
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 Arabic Mathematics  David Joyce; Dept. of Mathematics & Computer Science, Clark University
Resources on the history of Arabic mathematics, with a map, a list of mathematicians, sources, and a Bibliography.
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 Arabic mathematics: forgotten brilliance?  MacTutor Math History Archives
Linked essay exploring the debt we owe to Arabic/Islamic mathematics. In many respects the mathematics studied today is far closer in style to that of the Arabic/Islamic contribution than to that of the Greeks. Certainly many of the ideas previously thought
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 Arabic Numerals (Islam and Islamic History)  Nawwab, Speers, Hoye; Arabian American Oil Co.
The system of numeration employed throughout the greater part of the world today was probably developed in India, but because it was the Arabs who transmitted it to the West, the numerals it uses have come to be called Arabic. This page shows the early
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 The Arabic numeral system  MacTutor Math History Archives
Linked essay exploring the transmission of Indian numerals first to the Arabic/Islamic peoples and from them to Europe. The eastern and western parts of the Arabic world (North Africa and Spain) both saw separate developments of Indian numerals with relatively
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 Arbelos Internet Math Society  Bert Liberi and William F. Widulski, Westchester Communtiy College
A mathematics society dedicated to the pursuit of elegance in problemsolving. Every month, solve challenging problems that require "more imagination than memorization." Also, access old problems and solutions; and study a list of heuristics of problemsolving,
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 Archimedes  Chris Rorres, Drexel University
A collection of information on Archimedes' life and achievements, complete with historical quotes, illustrations, and animations. The site covers Archimedes' inventions and accomplishments: Archimedes' Claw, Burning Mirrors, the Golden Crown, the Archimedes
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 Archimedes' Laboratory  Gianni A. Sarcone and Marie J. Waeber
Archimedes' Laboratory invents, creates, and develops handson thinking games which help teach mathematical applications. They also create and manufacture original educational manipulatives and puzzles to support promotional activities. The resources
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 Archimedes Palimpsest  The Walters Art Gallery
An introduction to the people, places, times, and historical significance of the Archimedes Palimpsest, a compendium of mathematical treatises by Archimedes of Syracuse. The manuscript itself includes the only copy of the treatise Method of Mechanical
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 Archives of American Mathematics  The Dolph Briscoe Center for American History, The University of Texas at Austin
The only archival repository in the United States solely dedicated to collecting, preserving, and providing access to the records of American mathematicians and mathematical organizations for use by historians, mathematicians, educators, and others interested
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 ArcLessons  Environmental Systems Research Institute, Inc. (ESRI)
Lessons for using geographic information systems (GIS) in the classroom include X and Y Coordinates Rule the Map, Investigating Temperature Extremes in the USA, Baseball Radio Station Analysis, The Dust Bowl, The Great Migration, Japanese American Internment,
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 Area and Diameter  NASA Lewis Learning Technologies Project
Mrs. Bosley wants a big round piece of plastic to throw over her little boy's round sandbox to keep the sand clean. The sandbox has a diameter of 3 meters. Approximately how big will the round piece of plastic need to be? A detailed answer is provided.
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 Area and perimeter  Mark Motyka, Math League Multimedia
Definitions and illustrations: Area; Area of a square; Area of a rectangle; Area of a parallelogram; Area of a trapezoid; Area of a triangle; Area of a circle; Perimeter; Circumference of a circle.
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 Area and Perimeter (SMILE)  Monica Starks, John Fiske Elementary
A middle school lesson on measuring and calculating the area and perimeter of squares, rectangles, triangles, etc. From the Geometry and Measurement section of a collection of almost 200 single concept lessons by the Science and Mathematics Initiative
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 Area, Arithmetic and Algebra (SMILE)  Larry Freeman, Kenwood Academy
A lesson designed to show teachers how area of rectangles and squares can motivate the learning of multiplication rules for certain binomials; how students can perform arithmetic based on these identities; and several applications of the "distributive
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 Area of a Circle  Jon Seaton
Enter a radius, diameter, circumference, or area of a circle, and this simple JavaScript calculator returns all of those measures.
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 Area Of A Circle  Kuldeep Kaur
Lessons and worksheets to find the area of a circle. Kaur has posted stepbystep instructions through this blog, which dates back to December, 2011.
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 Area Under Curves: The Integral  Don Cohen (The Mathman)
Area on the geoboard; Plotting points on a computer or programmable calculator to find the area under curves; Finding the area under curves on graph paper. Sample problems with some answers and a program to plot points  from Chapter 13 of Don Cohen's
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 Are Mathematicians Turning Soft?  Keith Devlin (Devlin's Angle)
An article about 'soft mathematics'. "...In order to capture some of the abstract patterns and structures of mind and language, linguists sometimes find it convenient (perhaps necessary) to make use of mathematics, or at least mathematical notation or
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 Are You Better Than Average?  Todd Curtis
Dice game developed to quickly demonstrate some of the basics of probability. You'll need one pair of dice, a throwing tray or other flat surface, and a score sheet.
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 Arithmagic  Ivars Peterson (MathTrek)
Arthur T. Benjamin eschews the usual trappings of the magician's trade. Calling himself a mathemagician, he astonishes audiences with amazing feats of mental arithmetic. Behind the scenes, he reveals how you, too, can look like a genius without really
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 Arithmagic (MatheMUSEments!)  Ivars Peterson (Math Muse for Kids)
Prof. Arthur Benjamin amazes audiences by multiplying numbers in his head faster than someone using a calculator. Benjamin says that anyone  young or old  can learn to do the same feats of mental arithmetic. All it takes is a memory for numbers and
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 Arithmetic and Algebra  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
More than 110 games or puzzles having to do with arithmetic or algebra, with extensive discussions and solutions. Most require a browser capable of displaying JavaScript or Java.
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 Arithmetic and Algebra Review Problems  Alan Selby
Arithmetic and algebra review problems to help people check or diagnose arithmetic skills and other calculation or algebra skills. Includes a 20x20 times table.
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 Arithmetic CD  John Banfill
The Arithmetic CD contains over 1700 basic arithmetic lessons for K8 students. Each lesson has an explanation, some interactive practice, and challenge games. The lessons on the CD consist of interactive html files and require a web browser to operate.
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 Arithmetic  Math Forum
Links to some of the best Internet resources for arithmetic: classroom materials, software, Internet projects, and public forums for discussion.
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 Arithmetic with Roman Numerals  Jim Loy
"It is fairly obvious that Roman numerals are more difficult to use than our arabic numerals. They are fine for recording a date or indicating a chapter number. But, they make arithmetic somewhat difficult....Egypian numerals are essentially Roman numerals,
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 Aritm  Mikael Bonnier
A Java applet for simple mental calculation, drilling on basic arithmetic (addition, subtraction, multiplication, or division, with 1 or 2digit terms), in digits, words, or Roman numerals. It will tell you when your answer is wrong, and how many problems
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 The Arlington Algebra Project  Arlington Central School District
Exercises and homework, organized into twelve units, written by 25 Arlington math teachers from the LaGrangeville (NY) high school and middle schools.
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 Art and Mathematics  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about art and mathematics, such as "Do you know ways that art can be linked to mathematics?"
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 Arte Matemática  TV Cultura
Introducões, entrevistas, e programas sobre geometria, números, simetria, perspectiva, tempo, espaço, ritmo, beleza, ordem, caos, o número de ouro, Pítagoras, e mais. Com biografías curtas de autores e artistas.
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 Articulation in Mathematics Education  EXTEND  Perspectives in Mathematics Education
Links to articles on creating smoother transitions between education and work, between school and college and within sectors of higher education, and about preparing teachers to facilitate these transitions and students to respond to new environments.
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 Art Matrix Fractals  H. Smith, J. Staller
Some basic information about fractals; a fractal gallery; and a twohour video for sale on the subject of fractals and chaotic dynamical systems. What is a fractal?; Product line; Wholesale policy; Introduction to Fractals; etc.
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