# Joy of Mathematics

Course No. 1411
Professor Arthur T. Benjamin, Ph.D.
Harvey Mudd College
4.5 out of 5
195 Reviews
82% of reviewers would recommend this product
Course No. 1411
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### What Will You Learn?

• Reinvigorate your love of mathematics, and discover how the field can be enjoyed for its beauty and certainty.
• Learn the beautiful and unexpected properties of Fibonacci numbers, which show up in art, nature, and even poetry.
• Explore the bizarre concept of infinity, and deliberate over whether there are an infinite number of infinities.
• Examine the concepts of imaginary and complex numbers, which play a surprisingly useful role in physics.
• Study how mathematical proofs work, including proofs by deduction, proofs by induction, and proofs by existence.

## Course Overview

Ready to exercise those brain cells? Humans have been having fun with mathematics for thousands of years. Along the way, they've discovered the amazing utility of this field—in science, engineering, finance, games of chance, and many other aspects of life. This course of 24 half-hour lectures celebrates the sheer joy of mathematics, taught by a mathematician who is literally a magician with numbers. Professor Arthur T. Benjamin of Harvey Mudd College is renowned for his feats of mental calculation performed before audiences at schools, theaters, museums, conferences, and other venues.

Although racing a calculator to solve a difficult problem may seem like a superhuman achievement, Professor Benjamin shows that there are simple tricks that allow anyone to look like a math magician. Professor Benjamin has another goal in this course: throughout these lectures, he shows how everything in mathematics is connected—how the beautiful and often imposing edifice that has given us algebra, geometry, trigonometry, calculus, probability, and so much else is based on nothing more than fooling around with numbers.

Fun with Numbers

Here is an example:

Think of a number between 1 and 10. Triple it. Add 6. Then triple again. Now take your answer, probably a two-digit number, and add the digits of your answer. If you still have a two-digit number, add those digits again. You should now be thinking of the magical number 9. The reason this works is based on algebra and the fact that the digits of any multiple of 9 must sum to a multiple of 9.

This is one of the many wonders of modular arithmetic, sometimes called clock arithmetic, where numbers wrap around in a circle. A useful application of this field is casting out nines, a simple and ancient technique for checking the answers to arithmetical problems.

Modular arithmetic also provides a very handy method for mentally computing the day of the week for any date in history.

This connection between entertaining number tricks and the deeper properties of mathematics reflects Dr. Benjamin's specialty, which is combinatorics, the branch of mathematics that deals with the subtleties of counting. Some examples: How many different six-symbol license plates are possible? And for the book collector, how many ways are there of arranging 10 books on a shelf? (Would you believe more than 3 million?) These simple questions introduce concepts such as the factorial function.

Drawing on his dual fascination with combinatorics and games, Dr. Benjamin used his analytical skill to win first place in the American Backgammon Tour in 1997.

Have You Forgotten Math? Worry Not!

Professor Benjamin gives his presentation on the number 9 in—where else?—Lecture 9. Other lectures are devoted to pi, the imaginary number i, the transcendental number e, and infinity. These numbers are gateways to intriguing realms of mathematics, which you explore under Dr. Benjamin's enthusiastic guidance.

He also introduces you to prime numbers, Fibonacci numbers, and infinite series. And you investigate the powerful techniques for manipulating numbers using algebra, geometry, trigonometry, calculus, and probability in lectures that may hark back to subjects you studied in high school and college. You will find Dr. Benjamin's introduction to these fields both a useful refresher and a bird's-eye view of the most important areas of mathematics. Intriguingly, he approaches these topics from the novel perspective of combinatorics and mathematical games, providing a fun entry into subjects that are often taught in a lackluster way.

In the next-to-last lecture, you look at the application of probability to games. And finally, you splurge on feats of mathematical magic: For instance, did you know that you don't have to be a genius to calculate cube roots in your head?

Throughout the course, Dr. Benjamin assumes that you may have no more than a distant memory of high school math. He believes that it is his job to fan those embers into a burning interest in the subject he loves so much—and in which he takes such exquisite joy.

A Math Course Designed for You

This course is especially well suited for:

• Anyone attracted by Dr. Benjamin's promise of a joyful attitude to an often-imposing subject
• Anyone for whom high school and college math courses are a distant memory who would like to revisit these subjects to explore topics they skipped the first time
• Anyone now taking math who would like a big-picture perspective on the major areas of the field from a playful, joyous point of view
• Budding math mavens who love numbers and the magic that can be done with them.

Be prepared to encounter strange equations, novel ways of thinking, and symbols and computational methods that may be new to you. But also prepare to sharpen your wits in ways you never thought possible. Math is a challenging subject, but it pays immense rewards. Few people understand everything the first time through an unfamiliar domain of math. "But that's OK," says Dr. Benjamin. "You can rewind me and have me explain it all over again! All of this material bears repeating, and I hope you get to enjoy it many times over."

Patterns, Patterns Everywhere

One of Dr. Benjamin's greatest loves is the Fibonacci sequence, which shows up in many spheres of mathematics, as well as in nature, art, computer science, and poetry. The distinctive meter of a limerick encodes Fibonacci numbers, and Dr. Benjamin has even composed his own limerick to show how the sequence begins:

I think Fibonacci is fun;
Then 2, 3, 5, 8,
But don't stop there, mate!
The fun has just barely begun.

The series continues on: 13, 21, 34, 55, 89, … with each successive Fibonacci number being the sum of the previous two. This simple pattern is named for a 12th-century mathematician who described a problem involving imaginary rabbits that never die. Starting with a pair of baby rabbits, the animals take a month to mature, then mate and produce a male and a female; these mature after a month and mate, along with their parents. The total number of pairs after each month follows the Fibonacci sequence.

In our own day, Fibonacci numbers appear as a critical plot element in The Da Vinci Code, notably under the guise of the golden ratio, an ideal proportion favored by artists and architects that is intimately connected to the Fibonacci sequence. However, Dr. Benjamin cautions that the quest for instances of the golden ratio in nature can get out of hand.

A Feast for the Brain

Anyone who has ever witnessed a feat of mathematical prowess and chalked it up to unfathomable intellect will be interested to learn that there is often a simple shortcut at work. For example, the first 24 digits of pi, the famous ratio of the circumference of a circle to its diameter, can be memorized with the help of a silly sentence starting "My turtle Pancho …" Four more sentences take you to 100 digits, making you look like a prodigy indeed!

Similarly, if someone asked you to add up all the numbers from 1 to 100, you might take out a sheet of paper and start to work, little realizing that this difficult-looking problem can be done in your head in seconds by a method devised by the famous mathematician Carl Friedrich Gauss when he was a boy. The same goes for squaring and multiplying multidigit numbers in your head.

"Mathematics is food for the brain," says Dr. Benjamin. "It helps you think precisely, decisively, and creatively and helps you look at the world from multiple perspectives. Naturally, it comes in handy when you're shopping around for the best bargain or trying to understand the statistics you read in the newspaper.

"But I hope that you come away from this course with a new way to experience beauty—in the form of a surprising pattern or an elegant logical argument. Many people find joy in fine music, poetry, and other works of art—and mathematics offers joys that I hope you, too, will learn to experience. If Elizabeth Barrett Browning had been a mathematician, she might have said, ‘How do I count thee? Let me love the ways!'"

24 lectures
|  Average 30 minutes each
• 1
The Joy of Math—The Big Picture
Professor Benjamin introduces the ABCs of math appreciation: The field can be loved for its applications, its beauty and structure, and its certainty. Most of all, mathematics is a source of endless delight through creative play with numbers. x
• 2
The Joy of Numbers
How do you add all the numbers from 1 to 100—instantly? What makes a square number square and a triangular number triangular? Why do the rules of arithmetic really work, and how do you calculate in bases other than 10? x
• 3
The Joy of Primes
A number is prime if it is evenly divisible by only itself and one: for example, 2, 3, 5, 7, 11. Professor Benjamin proves that there are an infinite number of primes and shows how they are the building blocks of our number system. x
• 4
The Joy of Counting
Combinatorics is the study of counting questions such as: How many outfits are possible if you own 8 shirts, 5 pairs of pants, and 10 ties? A trickier question: How many ways are there to arrange 10 books on a shelf? Combinatorics can also be used to analyze numbering systems, such as ZIP Codes or license plates, as well as games of chance. x
• 5
The Joy of Fibonacci Numbers
The Fibonacci numbers follow the simple pattern 1, 1, 2, 3, 5, 8, etc., in which each number is the sum of the two preceding numbers. Fibonacci numbers have many beautiful and unexpected properties, and show up in nature, art, and poetry. x
• 6
The Joy of Algebra
Arguably the most important area of mathematics, algebra introduces the powerful idea of using an abstract variable to represent an unknown quantity. This lecture demonstrates algebra's golden rule: Do unto one side of an equation as you do unto the other. x
• 7
The Joy of Higher Algebra
This lecture shows how to solve quadratic (second-degree) equations from the technique of completing the square and the quadratic formula. The quadratic formula reveals the connection between Fibonacci numbers and the golden ratio. x
• 8
The Joy of Algebra Made Visual
Algebra can be used to solve geometrical problems, such as finding where two lines cross. The technique is useful in real-life problems, for example, in choosing a telephone plan. Graphs help us better understand everything from lines to equations with negative or fractional exponents. x
• 9
The Joy of 9
Adding the digits of a multiple of 9 always gives a multiple of 9. For example: 9 x 4 = 36, and 3 + 6 = 9. In modular arithmetic, this property allows checking answers by "casting out nines." A related trick: mentally computing the day of the week for any date in history. x
• 10
The Joy of Proofs
Professor Benjamin begins his discussion of mathematical proofs with intuitive cases like "even plus even is even" and "odd times odd is odd." He builds to more complex proofs by existence and induction, and ends with a checkerboard challenge. x
• 11
The Joy of Geometry
Geometry is based on a handful of definitions and axioms involving points, lines, and angles. These lead to important conclusions about the properties of polygons. This lecture uses geometric reasoning to derive the Pythagorean theorem and other interesting results. x
• 12
The Joy of Pi
Pi is the ratio of the circumference of a circle to its diameter. It starts 3.14 and continues in an infinite nonrepeating sequence. Professor Benjamin shows how to learn the first hundred digits of this celebrated number, making it look as easy as pie. x
• 13
The Joy of Trigonometry
Trigonometry deals with the sides and angles of triangles. This lecture defines sine, cosine, and tangent, along with their reciprocals, the cosecant, secant, and cotangent. Extending these definitions to the unit circle allows a handy measure of angle: the radian. x
• 14
The Joy of the Imaginary Number i
Could the apparently nonsensical number the square root of –1 be of any use? Very much so, as this lecture shows. Such imaginary and complex numbers play an indispensable role in physics and other fields, and are easier to understand than they appear. x
• 15
The Joy of the Number e
Another indispensable number to learn is e = 2.71828 ... Defined as the base of the natural logarithm, e plays a central role in calculus, and it arises naturally in many spheres of mathematics, including calculations of compound interest. x
• 16
The Joy of Infinity
What is the meaning of infinity? Are some infinite sets "more" infinite than others? Could there possibly be an infinite number of levels of infinity? This lecture explores some of the strange ideas associated with mathematical infinity. x
• 17
The Joy of Infinite Series
Starting with the analysis of the proposition 0.999999999 ... = 1, this lecture ex­plores what it means to add up an infinite series of numbers. Some infinite series con­verge on a definite value, while others grow arbitrarily large. x
• 18
The Joy of Differential Calculus
Calculus is the mathematics of change, and answers questions such as: How fast is a function growing? This lecture introduces the concepts of limits and derivatives, which allow the slope of a curve to be measured at any point. x
• 19
The Joy of Approximating with Calculus
Exploiting the idea of the derivative, we can approximate just about any function using simple polynomials. This lecture also shows why a formula sometimes known as "God's equation" (involving e, i, p, 1, and 0) is true, and how to calculate square roots in your head. x
• 20
The Joy of Integral Calculus
Geometry and trigonometry are used to determine the areas of simple figures such as triangles and circles. But how are more complex shapes measured? Calculus comes to the rescue with a technique called integration, which adds the simple areas of many tiny quantities. x
• 21
The Joy of Pascal's Triangle
A geometric arrangement of binomial coefficients called Pascal's triangle is a treasure trove of beautiful number patterns. It even provides an answer to the song "The Twelve Days of Christmas": Exactly how many gifts did my true love give to me? x
• 22
The Joy of Probability
Mathematics can draw detailed inferences about random events. This lecture covers major concepts in probability, such as the law of large numbers, the central limit theorem, and how to measure variance. x
• 23
The Joy of Mathematical Games
This lecture applies the law of total probability and other concepts from the course to predict the long-term losses to be expected from playing games such as roulette and craps and understand what is known as the "Gambler's Ruin Problem." x
• 24
The Joy of Mathematical Magic
Closing the course with a magician's flair, Professor Benjamin shows a trick for producing anyone's phone number, how to create a magic square based on your birthday, how to play "mathematical survivor," a technique for computing cube roots in your head, and a card trick to ponder. x

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##### Course Guidebook Details:
• 184-page course synopsis
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Arthur T. Benjamin, Ph.D.
Harvey Mudd College
Dr. Arthur T. Benjamin is Professor of Mathematics at Harvey Mudd College. He earned a Ph.D. in Mathematical Sciences from Johns Hopkins University in 1989. Professor Benjamin's teaching has been honored repeatedly by the Mathematical Association of America (MAA). In 2000, he received the MAA Deborah and Franklin Tepper Haimo National Award for Distinguished College or University Teaching of Mathematics. The MAA also named...
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## Reviews

Joy of Mathematics is rated 4.4 out of 5 by 195.
Rated 4 out of 5 by from Great idea wish I was smart enough to understand. Love math but math does NOT love me
Date published: 2020-02-24
Rated 4 out of 5 by from Intriguing A very good introduction or refreshment of some of the beauty that makes mathematics so very interesting and intriguing. I am not a mathematician but I do have a love for the enticement the course offers to explore beyond the introduction.
Date published: 2020-02-16
Rated 5 out of 5 by from Fun and interesting I recently bought the Joy of Mathematics course and have watched the first 5 lessons. Professor Benjamin does a good job explaining the concepts and makes the course truly fun.
Date published: 2020-02-11
Rated 5 out of 5 by from I feel like a kid in Junior High on Pie Day! I’m enjoying learning with no stress. That is pure joy.
Date published: 2020-02-11
Rated 5 out of 5 by from Title conveys it all, The Joy of Math! Instructor shares his love of math, and presents math concepts without judgment. I am only a few classes into the course, and I have already learned so much!
Date published: 2020-02-07
Rated 5 out of 5 by from Going to love this I have just watched the first lecture of the Math course. As an 80+ year old person, l am so looking forward to seeing and learning more of what I have missed by not going further than Algebra. Professor Benjamin will be a true delight and interesting instructor. He, truly, make learning a joy and exciting experience.The fact that I can rewatch each lecture is a real plus.
Date published: 2020-02-05
Rated 5 out of 5 by from Great course I bought this a couple weeks ago I am very happy with it.
Date published: 2020-01-24
Rated 5 out of 5 by from Learned things I din't know in Mathematics Let me say up front that Professor Benjamin is very animated and flails his arms about while he talks. At first, this was disconcerting to me. However, after the first two lectures I got use to how he speaks and found his method of teaching endearing. Professor Benjamin uses his gestures and facial expressions for emphasis, along with telling jokes, related to math. He can be quite funny. That said, I have had math all the way up to Differential Equations, in college. From this course, "The Joy of Mathematics", I learned many things that I had not heard or experienced in the lower math subjects and it was nice to get a refreshing review of the higher math subjects that I already knew. Each subject is well organized and leads into the other subjects. There are many examples, formulas and graphics to make the subjects easy to understand and, may I say, a joy to learn. Fibonacci sequences were one particular subject that Professor Benjamin is an expert in and manipulated this sequence in so many interesting ways that I had no idea the sequence was related to all kinds of other mathematics, besides sequences. Very interesting! Professor Benjamin explains simple topics, such as numbers and counting, along with primes, Pi, e, i, algebra, geometry, trig, calculus and many other mathematic subjects. Each subject was presented clearly and with examples of how they each can be used. The Calculus topics may be a little difficult to understand, if you haven't taken a Calculus course, but Professor Benjamin makes the subject matter about as easy as I have ever seen. If fact, he showed techniques that I have never seen, before, or at least, had forgotten years ago. I would highly recommend the "Joy of Mathematics" to anyone who has the interest and/or who wants a refresher course on many mathematic subjects.
Date published: 2020-01-07