viii Preface
Using the complex exponential function to simplify trigonometry is a compelling as-
pect of elementary complex analysis and geometry. Students in my courses seemed
to appreciate this material to a great extent.
One of the most appealing combinations of the geometric series and the expo-
nential series appears in Chapter 4. We combine them to derive a formula for the
sums
Xn
j=1
jp,
in terms of Bernoulli numbers.
We briefly discuss ordinary and exponential generating functions, and we find
the ordinary generating function for the Fibonacci numbers. We then derive Bi-
net’s formula for the n-th Fibonacci number and show that the ratio of successive
Fibonacci numbers tends to the golden ratio
1+

5
2
.
Fairly early in the book (Chapter 3) we discuss hyperbolas, ellipses, and parabo-
las. Most students have seen this material in calculus or even earlier. In order to
make the material more engaging, we describe these objects by way of Hermitian
symmetric quadratic polynomials. This approach epitomizes our focus on complex
numbers rather than on pairs of real numbers.
The geometry of the unit circle also allows us to determine the Pythagorean
triples. We identify the Pythagorean triple (a,b,c) with the complex number
a
c
+i
b
c
;
we then realize that a Pythagorean triple corresponds to a rational point (in the first
quadrant) on the unit circle. After determining the usual rational parametrization
of the unit circle, one can easily find all these triples. But one gains much more; for
example, one discovers the so-called
tan(θ
2
) substitution from calculus. During the
course several students followed up this idea and tracked down how the indefinite
integral of the secant function arose in navigation.
This book is more formal than was the course itself. The list of approximately
two hundred eighty exercises in the book is also considerably longer than the list
of assigned exercises. These exercises (as well as the figures) are numbered by
chapter, whereas items such as theorems, propositions, lemmas, examples, and
definitions are numbered by section. Unless specified otherwise, a reference to
a section, theorem, proposition, lemma, example, or definition is to the current
chapter. The overall development in the book closely parallels that of the courses,
although each time I omitted many of the harder topics. I feel cautiously optimistic
that this book can be used for similar courses. Instructors will need to make their
own decisions about which subjects can be omitted. I hope however that the book
has a wider audience including anyone who has ever been curious about complex
numbers and the striking role they play in modern mathematics and science.
Chapter 1 starts by considering various number systems and continues by de-
scribing, slowly and carefully, what it means to say that the real numbers are
a complete ordered field. We give an interesting proof that there is no rational
square root of 2, and we prove carefully (based on the completeness axiom) that
positive real numbers have square roots. The chapter ends by giving several possible
definitions of the field of complex numbers.
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