 Dissection (The Geometry Junkyard)  David Eppstein, Theory Group, ICS, UC Irvine
An extensive annotated list of links to material on problems of cutting a region (such as a polygon into the plane) into pieces (possibly putting them together to form a different polygon). Related topics include tiling (in which the whole plane is cut
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 Distance Calculator Between Cities  Dan Gallagher
Enter two cities or countries and this CGI illustrates them on a scaled political map, calculates the distance between the two locations in miles and kilometers, and provides information about latitude, longitude, bearing, and airports. All latitude and
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 Distance Calculus @ Suffolk University  Suffolk University and MathMonkeys, LLC
Calculus on the Web. Contents include: PreCalculus (functions, algebra, trigonometry); Calculus Topics (differential and integral calculus, sequences and series, multivariable calculus, differential equations); Assistance (student, instructor); Curriculum
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 Distance Learning  Pure Science and Mathematics  Distance Learning Course Finder
A directory for those interested in finding out about online learning programs, courses, and seminars offered by a broad spectrum of educational providers. From the home page in addition to searching by subject you may also search by keyword or course
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 Distance, Rate, and Time  Math Forum, Ask Dr. Math FAQ
Distance = Rate x Time: A discussion and two problems.
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 Distance Recipe (Geometry and the Imagination)  Conway, Doyle, Gilman, Thurston; The Geometry Center
A technical definition of how to compute distance. Examples of distances; The Unit Disc Model; Passing from one model to another...
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 Distances on the surface of a cubical box  Henry Bottomley
An applet that demonstrates distances across the surface of a rectangular box. The first three boxes are the dimensions of the cuboid. To change them, type new numbers in and then press the "You choose" button. The text box offers six almost selfexplanatory
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 Distribution Curves (MSTE)  University of Illinois at UrbanaChampaign
A statistics lesson on the properties and calculations associated with a distribution curve, the shape of a data set when displayed on a histogram. Although this lesson focuses on Normal distribution curves, it is important to be familiar with the shapes
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 The Distribution of the Knight  the Theoretical Research Institute
For every given starting point in the knight's tour problem, evaluate every
possible path that visits each square exactly once, and then count how many
solutions exist. Illustrations and calculations of the distribution of solutions
and dead ends across
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 Divide and conquer for quantum computers  Ivars Peterson  Science News Online
In theory, quantum computations can be speeded up significantly by letting many quantum computers work together in parallel on data encoded as particles in an entangled quantum state.
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 Divide!  Andrew Starr
A web page used to demonstrate that if you divide any two integers, eventually the decimals will repeat.
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 Dividing 12foot Boards  NASA Lewis Learning Technologies Project
Lewis needs 1,500 boards to build a small rocket. Each board must be 3 feet long. If boards are sold in 12 foot lengths, how many boards must Lewis buy and cut into 3 foot pieces to get the 1,500 he needs? A detailed answer is provided. From NASA's 9th
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 Dividing by 0  Math Forum, Ask Dr. Math FAQ
Why can't you divide by 0? Why is 0/0 "indeterminate" and 1/0 "undefined"? Why is dividing by zero "illegal"?
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 Dividing Decimals  NASA Lewis Learning Technologies Project
Dividing decimals: What is 12.8 divided by .04? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Dividing: Fractions and Mixed Numbers  NASA Lewis Learning Technologies Project
What is 1 1/2 divided by 1/2? A detailed answer is provided. From NASA's 9th Grade Math Proficiency Test.
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 Dividing The Plane  Jim Loy
A line divides the plane into two pieces (regions). Draw another line. The plane is now divided into three or four regions. It is three regions if the lines are parallel, four if they intersect. A third line divides the plane into seven regions. Find
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 Divisibility Rules  Calculation Tips & Tricks, The Math Forum
Tips for figuring out whether a number can be divided by the numbers 313, with a Spanish translation and an explanation of why the rules work by Robert L. Ward.
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 Divisibility Rules  Math Forum, Ask Dr. Math FAQ
How can you tell whether a number is divisible by another number (leaving no remainder) without actually doing the division? Why do 'divisibility rules' work?
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 Divisibility Rules to 50 and Beyond  Stephen D.T. Froggatt; Math Forum, Ask Dr. Math FAQ
A quick way of testing primality of larger numbers: the idea of deleting the last digit and adding or subtracting a multiple of the digit from the remaining number can be generalized to test for divisibility by prime numbers up to 50 and beyond.
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 Division by Zero  Dave Richeson
A blog about "math, puzzles, teaching, and academic technology." Posts, which date back to September of 2008 and sometimes introduce original applets, have included "Volumes of ndimensional balls," "Albrecht Dürer's ruler and compass constructions,"
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 Division with Roman Numerals  Jim Loy
Roman numeral division can be very easy or fairly difficult, depending on the two numbers. An example of division by pieces, and a general method using repeated subtraction.
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 Divisor Plot  Jeffrey Ventrella
"We hear of primes described as the 'building blocks' of all numbers. Let's turn that concept on [its] head. Instead, let's think of primes as the negative spaces behind complex objects. Imagine a series of picket fences stacked in front of each other.
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 DIY Calculator  Clive (Max) Maxfield and Alvin Brown
Order the book How Computers Do Math, or preview its table of contents. The book's interactive laboratories guide you in the creation of a simple calculator program to run on your DIY Calculator; its accompanying CDROM contains a virtual "DoitYourself
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 DLK MathsWork Software
Selfdifferentiating, topicspecific math software for Windows 3.1 and above, on number, shape and space, and data handling. All of the practice modules have on screen monitoring at three levels. Six problem modules designed to improve users' application
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 DNA Adds Up  Ivars Peterson (MathLand)
Calculating that 0 + 0 = 0, 1 + 0 = 1, and 0 + 1 = 1 is normally no big deal. When the calculations are done in the lab using DNA molecules, however, these elementary manipulations look considerably more interesting. In the July 12 [1996] Science, a team
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 DNA, Computers, and Killer Apps  Ivars Peterson (MathLand)
When computer scientists look at DNA, they see information storage and processing. They view the four bases of DNA as something akin to the zeros and ones of the binary code by which computers store and process information. They look for algorithms, theorems,
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 Dodecahedron Measures  Paul Kunkel
An investigation of the formulas of the surface area and volume for the dodecahedron. With icosahedron extensions.
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 Does March Madness need a timeout?  J. Travis  Science News Online
Suggestions about the effects of circadian rhythms, daily cycles of physiological activity that every organism experiences, and changes in time zone (causing 'jet lag'), on sports teams.
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 Does the Number e have Special Meaning?  Spencer, Chan; Univ. of Toronto Mathematics Network
Answers, explanations, and expositions of the question, Does the number e have any real physical meaning, or is it just a mathematical convenience? Addresses the topics: Simple and Compound Interest; A Physical Meaning for the Number e; The General Situation;
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 Doing Mathematics  Bryan Meyer
Blog by an eleventh grade math teacher at a projectbased learning (PBL) school pursuing a Masters Degree in Teacher Leadership. Posts, which date back to February, 2012, have included "What Bowflex Can Teach Us about Assessment," "Habits of a Mathematician,"
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 Domain and Range of a Function  Math Forum, Ask Dr. Math Common Question
A selection of answers to questions about the domain and range of a function, as well as determining the domain and range of a function from its graph.
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 Domebook  Tom Camilli
Cardboard and transparent plastic geodesic domes built by children. Students start by constructing paper models, then apply scale factors to construct domes of any size using cardboard or wooden dowels and plastic sheeting. See pictures of classroom projects;
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 Dominoes Activity  Suzanne Alejandre
A classroom activity (similar to Pentomino + 1 = Hexomino; a variation on polyominoes) aligned to the NCTM and California Standards, to be explored through manipulatives (paper dominoes). Students explore whether it is possible to cover a 6x5 grid with
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 Donald Coxeter, Mathematician and Geometer  Great Canadian Scientists (GCS)
Harold Scott MacDonald Coxeter, Professor Emeritus, Math Dept., Univ. of Toronto, is best known for his work in hyperdimensional geometries and regular polytopes  geometric shapes that extend into the 4th dimension and beyond. In 1926 he discovered a
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 donalduncan's Channel
Narrated paper and pencil instructional videos  some, specific to British Columbia's Foundations of Math and Precalculus exams  on number, line segments and lines, rational expressions, factoring, quadratic functions, functions, exponents, polynomials,
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 Don Knuth's Home Page  Donald E. Knuth, Stanford University
From the author of The Art of Computer Programming. "Computer Musings" chronologically documents Knuth's informal lectures at Stanford. It also links to Musings Online, digitized versions of videos from the lecture series that included Dancing Links;
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 Don't Hate No Math  Elio Motella
Advice for students, parents, and teachers. The document called "Lecture" includes sections such as "The causes of your troubles," "It's called metacognition," and "Mental models and propositional representations"; see in particular Part D, titled "An
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 Doodal  Neil Thapen
Draw fractals freehand using a computer mouse: select a "brush size" to specify width in pixels, then click and drag in the large orange frame, the contents of which get copied in however many blue frames you specify. To rotate a blue box, click it while
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 Doodling and Miracles  Cut the Knot!, Alexander Bogomolny
Almost 100 years ago, Frank Morley proved a curious theorem from elementary geometry that had remained unknown until 1899. With time, the theorem became known in mathematical folklore as Morley's Miracle (Morley's Trisector Theorem is a more mundane term.)
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 The DOR: Home of the Direct Opposite Reverse  David P. Sterner
Sterner developed this shape, which he calls a geometric "missing link", and has applications as a lens.
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 Doron Zeilberger's Electronic Headquarters
Doron Zeilberger researches combinatorics using computer programs. The site is notable for his Opinions page; these opinions are wideranging but touch upon mathematics education, the use of computers, and the value of incomplete proofs. All of Zeilberger's
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 Do software engineers need mathematics?  Keith Devlin (Devlin's Angle)
Software engineers don't use their college mathematics, but they make use of their college mathematics education every day. Brains are perhaps the world's best examples of an adaptive system. When we subject the human brain to an extended educational
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 Do the Math  Slate
A topical series about math in culture, politics, psychology, and other popular themes, many written by math professor Jordan Ellenberg. Articles, which date back to June, 2001, have included "Barry Bonds and the Placebo Effect," "Algebra for Adulterers,"
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 Dot Patterns and Sierpinski Gasket  Cut the Knot!, Alexander Bogomolny
How many ways are there to define the Sierpinski gasket (also, the Sierpinski triangle)? The author has counted a respectable 9 but would be happy to learn of more. An applet with rows of digits or circles with colors corresponding to the digits shows
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 Dots and Boxes  Ivars Peterson (MathTrek)
The familiar pencilandpaper game of DotsandBoxes can be played on several different levels of sophistication. Elwyn Berlekamp posits that the game can be played on at least four different levels. "Players at any level consistently beat players at
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 Double Bubble Conjecture Proved (Math Chat)  Frank Morgan, MAA Online
Four mathematicians have announced a mathematical proof of the Double Bubble Conjecture: that the familiar double soap bubble is the optimal shape for enclosing and separating two chambers of air. In an address to the Undergraduate Mathematics Conference
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 Doubling Pennies  Math Forum, a Classic Problem from the Ask Dr. Math FAQ
Which is more, a million dollars or a penny doubled every day?
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 Doubling the Cube  MacTutor Math History Archives
Linked essay covering the history of and some solutions to the classical
problem in Greek mathematics of doubling or duplicating the cube, also called the
Delian problem; and on proving the impossibility of constructing a solution using only ruler
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 Doug's Home Page  Douglas J. Ingalls
Includes mathematical interests such as images of fractal applications of Newton's Method and Gibb's Phenomena, with related programs in FORTRAN and BASIC, a discussion of the apparent depth problem in optics, and how multiple decisions can be reduced
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 Downloadable Articles, Papers & Materials  Michael de Villiers; Mathematics Education, Univ. of DurbanWestville, South Africa
Articles by Villiers related to geometry and geometry education some in PDF format, including: An Extended Classification of Quadrilaterals; A Mathematical Treasure Hunt; Place Kicking Locus in Rugby; Sketchpad Solutions and Results; A Dual, and Generalizations,
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