 A Proof of the Pythagorean Theorem  Isaac Reed
One of the most famous theorems in mathematics, the Pythagorean theorem has many proofs. Presented here is one that relies on Euclidean algebraic geometry and is thus beautifully simple.
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 Proof of the Pythagorean Theorem (Math Exploration Quilt)  Rik Littlefield; Hanford School
Proof by the scaling law.
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 Proof of the Pythagorean Theorem  Rik Blok
Pythagorean theorem: in a right triangle the square of the hypotenuse is equal to the sum of the squares of the sides containing the right angle. Two proofs: one by a construction, and one by the method of similar triangles.
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 Proofs in Mathematics  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A discussion of the value of proofs in the classroom, followed by a collection of proofs classified as either simple or charming. Simple proofs: Number of vowels in a Lewis Carroll game; Pigeonhole Principle; Number of X's and O's; Coloring points in
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 Proofs  James Garner
An essay on different approaches using mathematical proofs: inductive reasoning, reasoning by analogy, deductive reasoning, direct method, contrapositive approach, etc.
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 Proofs Wiki  Brunner Nathan
A communitybased collection of definitions, proofs, and theorems. The Proofs Wiki composition interface supports LaTeX and tooltips.
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 Proofs Without Words  Cut the Knot!, Alexander Bogomolny
Martin Gardner wrote, "There is no more effective aid in understanding certain algebraic identities than a good diagram. One should, of course, know how to manipulate algebraic symbols to obtain proofs, but in many cases a dull proof can be supplemented
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 A Proof that e is Irrational  Isaac Reed
A proof by contradiction that relies on the expression of e as a power series.
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 A Proof That e is Transcendental  Travis Kidd
A proof by contradiction, adapted from Klein, Famous Problems (New York: Chelsea Publishing Company, 1962).
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 Proof: The Sum of Prime Twins is Divisible by 12  Mathematics Dept., College of Marin
Prime twins are prime numbers that are two numbers apart. For example 41 and 43 are prime twins. Can you PROVE that the sum of prime twins is divisible by 12?
(This proof doesn't work for the prime twins 3 and 5.)
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 ProofWiki  Matt Westwood
ProofWiki is an online compendium of mathematical proofs. Those interested in adding to the work are urged to create an account and contribute.
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 Properties Glossary  Math Forum, Ask Dr. Math FAQ
What is an operation? What is an identity? What are the associative, commutative, and distributive properties? What is the property of closure? What is the inverse of something?
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 Properties of Dice  Klaus Mogensen
An essay on Proper Dice (illustrated) and Dice Roll Probabilities.
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 Properties of Numbers (SMILE)  Leon Steinfelds, King High School
A lesson that contrasts the "mean" behavior of 0, 1, 2, and regular numbers, likening numbers to students. From the "Miscellaneous" section of a collection of almost 200 single concept lessons by the Science and Mathematics Initiative for Learning Enhancement.
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 Properties Of Quadrilaterals (SMILE)  Margaret A. Olson, Morgan Park High School
A lesson designed to teach the names, definitions, and properties of quadrilaterals, and how to apply the correct property to each different quadrilateral. From the Geometry and Measurement section of a collection of almost 200 single concept lessons
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 Prophet of Chaos  Ivars Peterson (MathTrek)
"'...it may happen that small differences in the initial conditions produce very great ones in the final phenomena. A small error in the former will produce an enormous error in the latter. Prediction becomes impossible, and we have the fortuitous phenomenon.'
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 ProRadian  Jennifer Silverman
Protractors for learning about radians "in the same way you learned about degrees — by measuring." ProRadian learning sets contain two protractors, one scaled in 0.1 radians and one scaled in π/24 radians. Silverman, who now writes math curriculum
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 The Pros and Cons of Technology in the Classroom  Roy Pea, Larry Cuban, Bay Area School Reform Collaborative, TAPPED IN
Nationally recognized experts on the subject, Dr. Roy Pea and Dr. Larry Cuban offer their insights in this transcript of speeches each gave to a gathering of organizations that fund school reform projects. A transcript of questions and answers from the
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 Proudnerd.com  Heather Sable
"For the selfassured nerd": humorous tshirts, long sleeve tshirts, women's tshirts, sweatshirts, hooded sweatshirts, boxer shorts, hats and caps, bags and backpacks, mugs and cups, mousepads, apparel for kids, babies, and toddlers, and more. Solve
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 Prove it! Math Academy  Monks Math Ltd.
A residential summer math camp at Colorado State University for talented students 1418 years old. The twoweek course of Prove it! emphasizes mathematical rigor and proofwriting skills in a problemsolving context. Admissions begin with a test of word
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 ProveIt! TwoColumn Proofs Practice Tool  Michael Ferraro
Michael Ferraro of Balboa High School in San Francisco, CA, created this tool for students to practice their twocolumn proof skills. Choose a topic to begin, and choose statements and reasons from the list given. As you go, there are options to remove
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 Providing HandsOn, MindsOn, and Authentic Learning Experiences in Mathematics (NCREL)  Cathy Cook; Pathways to School Improvement
A linked essay giving overview, background, and issues around constructivist theory and its implementation. "When educators begin to see learning as knowledge construction, they change their thinking about curriculum, instruction, and assessment, developing
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 PseudoNumerals  phonetic symbols for numbers  Allan Krill
A method for remembering IDnumbers, etc., as words. The techniques used here have been used for 200 years, but now are formally defined as numerals. Presented in August at Mathfest 2002.
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 Psychosemiotic Theory and Educational Practice  Alice Leonard
Walkerdine and Corran's (1979) paper showed how psychosemiology may account for developmental data as a potentially fruitful alternative to the better known stage theories, like that of Piaget. They argued that learning mathematics is an ideal activity
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 P.T. Chang
Articles by this math professor from the University of Alaska Anchorage's MatSu College include "The Ostentatious World of Algebra," "InService Training for the Math Teacher of the 21st Century," and "Retesting in a College Remedial Mathematics Course."
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 PTC: Product Lifecycle Management Software  Parametric Technology Corporation
PTC acquired MathSoft, developer of Mathcad and other software for math, science and engineering for business, research, academic and government markets. They also market Pro/ENGINEER, Windchill, Arbortext, ProductView, CoCreate, and InSight.
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 Ptolemy's Ptools  ThinkQuest 1998
Easytounderstand math projects for students to do by themselves or with adult direction. Triangle investigations of the perspectives of the 3D video games Star Fleet Academy, Quake II, and Sub Culture Submarine Adventure. "Quadrant projects" involve
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 P Torres blogger  Paula Torres
Blog by an AP Calculus teacher at a public high school in Rancho Cucamonga (CA). Posts, which date back to February, 2014, have included "Beginning to flip," "The wonder of Desmos," "Calculus around the room and 'the Statistics talk,'" "They won't fall
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 Publications and Research Tools (AMS)  American Mathematical Society
The AMS research and publishing services include MathSciNet and the AMS Electronic Journals. Research tools for mathematicians include Mathematical Reviews Author Lookup, Institution Codes and Addresses, Serials Abbreviations; the AMS Preprint Server,
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 Public Domain Materials  Mike Jones
A collection of public domain instructional and expository materials from a USborn math teacher who teaches in China. Microsoft Word and PDF downloads include a monthly circular consisting of short problems, "The BowandArrow Problem," and "Twinkle
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 Public Outreach, Education, Teaching and Reaching Youth (POETRY)  Sten Odenwald, National Aeronautics and Space Administration (NASA)
The goal of the IMAGE mission's education and public outreach program (POETRY) is to explain how solar storms affect the Earth, and to correct misconceptions about Earth's magnetic field, its radiation belts, and why we have aurora. Read the latest information
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 Public Understanding of Mathematics  Key Issues in Mathematics at the Math Forum
Links to organizations and articles that explore perceptions and assumptions nonmathematicians hold about mathematics and mathematicians.
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 The Published Data of Robert Munafo  Robert Munafo
Mathematical data includes MuEncy, The Encyclopedia of the Mandelbrot Set (History, Exploring, Area, Algorithms, Naming, etc), properties of specific numbers, such as 2.68542 . . . and 143, and very large numbers and ways to write them. Programs include
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 Publishing or Programming? A Framework for the Development and Presentation of Work by Children on the World Wide Web  Judy Keiner
A paper to be presented at SIGGRAPH97, Los Angeles, August 8th 1997, involving process writing approaches, and including three criteria for evaluating Web pages. Also links to example sites.
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 PUERTRA  Javier Sánchez González
The software package PUERTRA implemented a theoretical study of formal properties of Islamic geometrical art. PUERTRA modeled the Islamic rectilinear interlaced lattices found extensively in wood work (artesonado ceilings, mosque minbars, doors and windows,
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 Punctured Polyhedra  Ivars Peterson (MathTrek)
A tetrahedron has four triangular faces, four vertices, and six edges. When a vertex of one tetrahedron pierces the face of a second tetrahedron it forms a new, more complicated polyhedron: one triangular face has a triangular "hole" where the face was
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 PuraMate
Ejercicios e soluciones de ecuaciones de primer grado, ecuaciones de segundo grado, algebra de Baldor, polinomios, producto y cociente notable, binomios, trinomios, desigualdades, y inecuaciones. Un blog empezó en octubre, 2014, tiene entradas
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 Pure Math Online
Pure Math Online uses live, personal tutors to help students with algebra and other math homework in real time over the Internet. Program information and signup for free demo are available on the site.
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 Purplemath  Your Algebra Resource  Elizabeth Stapel
Algebra modules provide lessons, practical tips, hints, worked examples, and point out common mistakes in basic triangle length (trigonometry) values, calculators (what model to buy), canceling units, domain and range, exponents, factoring quadratics,
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 Putnam Exams  Dave Rusin
Solution sets and comments compiled from postings on the sci.math newsgroup. Online resources and citations for exams dating back to 1987.
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 PuzzleBeast  James W. Stephens
A collection of computergenerated puzzles, some illustrated with Java applets, some with solutions included: The Fried Okra Perplexity, A Dozen Irritating Sliding Block Puzzles, The Bulbous Blob Puzzle, Meandering Monk Maze, The Kung Fu Packing Crate
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 Puzzle Choice
A wide choice of puzzles and games for all ages, including crosswords, wordsearches, brainteasers, number puzzles (a calculator is provided), logics, teacher resources and other online games, including mazes.
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 Puzzle explorer  Wade Philpott
Links to mathematical games invented by Philpott and now for sale: Multimatch and Leap (originally Sweep).
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 Puzzle Fun  Rodolfo Kurchan
An online newsletter edited by Rodolfo Kurchan (Buenos Aires  Argentina) about polyominoes and other puzzles. Back issues are on the Web.
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 Puzzlemaker  Discovery Education
A puzzle generation tool for teachers, students and parents. Create and print customized puzzles, including math squares and number blocks, online, or buy a CD with editing tools and other extras.
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 Puzzle of the Week  Ralph Grove
A small archive of math and word puzzles having to do with patterns, permutations, and probability, with solutions, from a professor of computer science at Indiana University of Pennsylvania.
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 Puzzle Page  The Black Stump Ltd.
More than 150 links to puzzle sites on the Web. A new site is added each week.
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 Puzzler  Franklin Institute Online
Puzzles from the inQuiry Almanack Puzzle Archive: e.g. Cryptograms, January, 1998. Coded messages hide famous quotations. A clue is offered to begin breaking the code, and an answer key is provided. One puzzle a month from March of 1995 through July of
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 Puzzlers  Bryan Clair, University of Chicago
A collection of Clair's favorite puzzles (no discussion or answers are provided): The Nine Dots; Weighing Coins; The Dollar Hotel, Planning an Orchard; The Math Department; Tea and Cream; Bugs on a Square; River Crossing; More Crawling Bugs; The Unexpected
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 Puzzles
A blog of math puzzles. Post your answers in the comments sections.
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