# The Joy of X: A Guided Tour of Math, from One to Infinity

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## Book Preface

I have a friend who gets a tremendous kick out of science, even though he’s an artist.
Whenever we get together all he wants to do is chat about the latest thing in psychology or
quantum mechanics. But when it comes to math, he feels at sea, and it saddens him. The
strange symbols keep him out. He says he doesn’t even know how to pronounce them.
In fact, his alienation runs a lot deeper. He’s not sure what mathematicians do all day, or
what they mean when they say a proof is elegant. Sometimes we joke that I should just sit
him down and teach him everything, starting with 1 + 1 = 2 and going as far as we can.
Crazy as it sounds, that’s what I’ll be trying to do in this book. It’s a guided tour through
the elements of math, from preschool to grad school, for anyone out there who’d like to have
a second chance at the subject—but this time from an adult perspective. It’s not intended to
be remedial. The goal is to give you a better feeling for what math is all about and why it’s
so enthralling to those who get it.

We’ll discover how Michael Jordan’s dunks can help explain the fundamentals of calculus. I’ll show you a simple—and mind-blowing—way to understand that staple of geometry,
the Pythagorean theorem. We’ll try to get to the bottom of some of life’s mysteries, big and
small: Did O.J. do it? How should you flip your mattress to get the maximum wear out of it?
How many people should you date before settling down? And we’ll see why some infinities
are bigger than others.

Math is everywhere, if you know where to look. We’ll spot sine waves in zebra stripes,
hear echoes of Euclid in the Declaration of Independence, and recognize signs of negative
numbers in the run-up to World War I. And we’ll see how our lives today are being touched
by new kinds of math, as we search for restaurants online and try to understand—not to men-
tion survive—the frightening swings in the stock market.

By a coincidence that seems only fitting for a book about numbers, this one was born on
the day I turned fifty. David Shipley, who was then the editor of the op-ed page for the New
York Times, had invited me to lunch on the big day (unaware of its semicentennial signific-
ance) and asked if I would ever consider writing a series about math for his readers. I loved
the thought of sharing the pleasures of math with an audience beyond my inquisitive artist
friend.

“The Elements of Math” appeared online in late January 2010 and ran for fifteen weeks.
In response, letters and comments poured in from readers of all ages. Many who wrote were
students and teachers. Others were curious people who, for whatever reason, had fallen off
the track somewhere in their math education but sensed they were missing something worth-
while and wanted to try again. Especially gratifying were the notes I received from parents
thanking me for helping them explain math to their kids and, in the process, to themselves.

Even my colleagues and fellow math aficionados seemed to enjoy the pieces—when they
weren’t suggesting improvements (or perhaps especially then!).
All in all, the experience convinced me that there’s a profound but little-recognized hun-
ger for math among the general public. Despite everything we hear about math phobia,
many people want to understand the subject a little better. And once they do, they find it

The Joy of x is an introduction to math’s most compelling and far-reaching ideas. The
chapters—some from the original Times series—are bite-size and largely independent, so
feel free to snack wherever you like. If you want to wade deeper into anything, the notes at
the end of the book provide additional details and suggestions for further reading.
For the benefit of readers who prefer a step-by-step approach, I’ve arranged the material
into six main parts, following the lines of the traditional curriculum.

Part 1, “Numbers,” begins our journey with kindergarten and grade-school arithmetic,
stressing how helpful numbers can be and how uncannily effective they are at describing
the world.

Part 2, “Relationships,” generalizes from working with numbers to working with rela-
tionships between numbers. These are the ideas at the heart of algebra. What makes them
so crucial is that they provide the first tools for describing how one thing affects another,
through cause and effect, supply and demand, dose and response, and so on—the kinds of
relationships that make the world complicated and rich.

Part 3, “Shapes,” turns from numbers and symbols to shapes and space—the province
of geometry and trigonometry. Along with characterizing all things visual, these subjects
raise math to new levels of rigor through logic and proof.

In part 4, “Change,” we come to calculus, the most penetrating and fruitful branch of
math. Calculus made it possible to predict the motions of the planets, the rhythm of the
tides, and virtually every other form of continuous change in the universe and ourselves. A
supporting theme in this part is the role of infinity. The domestication of infinity was the
breakthrough that made calculus work. By harnessing the awesome power of the infinite,
calculus could finally solve many long-standing problems that had defied the ancients, and
that ultimately led to the scientific revolution and the modern world.

Part 5, “Data,” deals with probability, statistics, networks, and data mining, all relatively
young subjects inspired by the messy side of life: chance and luck, uncertainty, risk, volat-
ility, randomness, interconnectivity. With the right kinds of math, and the right kinds of
data, we’ll see how to pull meaning from the maelstrom.

As we near the end of our journey in part 6, “Frontiers,” we approach the edge of math-
ematical knowledge, the borderland between what’s known and what remains elusive. The
sequence of chapters follows the familiar structure we’ve used throughout—numbers, relationships, shapes, change, and infinity—but each of these topics is now revisited more
deeply, and in its modern incarnation.

I hope that all of the ideas ahead will provide joy—and a good number of Aha! moments.
But any journey needs to begin at the beginning, so let’s start with the simple, magical act
of counting

Title Page
Preface
Part One NUMBERS
1. From Fish to Infinity
2. Rock Groups
3. The Enemy of My Enemy
4. Commuting
5. Division and Its Discontents
6. Location, Location, Location
Part Two RELATIONSHIPS
7. The Joy of x
9. My Tub Runneth Over
11. Power Tools
Part Three SHAPES
12. Square Dancing
13. Something from Nothing
14. The Conic Conspiracy
15. Sine Qua Non
16. Take It to the Limit
Part Four CHANGE
17. Change We Can Believe In
18. It Slices, It Dices
20. Loves Me, Loves Me Not
21. Step Into the Light
Part Five DATA
22. The New Normal
23. Chances Are
24. Untangling the Web
Part Six FRONTIERS
25. The Loneliest Numbers
26. Group Think
27. Twist and Shout
28. Think Globally
29. Analyze This!
30. The Hilbert Hotel
Acknowledgments
Notes
Credits
Index