Sources in the Development of Mathematics pot

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Sources in the Development of Mathematics
The discovery of infinite products by Wallis and infinite series by Newton marked the
beginning of the modern mathematical era. The use of series allowed Newton to find
the area under a curve defined by any algebraic equation, an achievement completely
beyond theearlier methodsof Torricelli, Fermat,and Pascal. The workof Newtonand
his contemporaries, including Leibniz and the Bernoullis, was concentrated in math-
ematical analysis and physics. Euler’s prodigious mathematical accomplishments
dramatically extended the scope of series and products to algebra, combinatorics, and
number theory. Series and products proved pivotal in the work of Gauss, Abel, and
Jacobi in elliptic functions; in Boole and Lagrange’s operator calculus; and in Cayley,
Sylvester, and Hilbert’s invariant theory. Series and products still play a critical role
in the mathematics of today. Consider the conjectures of Langlands, including that of
Shimura-Taniyama, leading to Wiles’s proof of Fermat’s last theorem.
Drawing on the original work of mathematicians from Europe, Asia, and America,
Ranjan Roy discusses many facets of the discovery and use of infinite series and
products. He gives context and motivation for these discoveries, including original
notation and diagrams when practical. He presents multiple derivations for many
important theorems and formulas and provides interesting exercises, supplementing
the results of each chapter.
Roy deals with numerous results, theorems, and methods used by students,
mathematicians, engineers, andphysicists. Moreover,since he presents originalmath-
ematical insights often omitted from textbooks, his work may be very helpful to
mathematics teachers and researchers.
ranjan roy is the Ralph C. Huffer Professor of Mathematics and Astronomy at
Beloit College. Roy has published papers and reviews in differential equations, fluid
mechanics, Kleinian groups, and the development of mathematics. He co-authored
Special Functions (2001) with George Andrews and Richard Askey, and authored
chapters in the NIST Handbook of Mathematical Functions (2010). He has received
the Allendoerfer prize, the Wisconsin MAA teaching award, and the MAA Haimo

award for distinguished mathematics teaching.
Cover image by NFN Kalyan; Cover design by David Levy.

Sources in the Development
of Mathematics
Infinite Series and Products from the
Fifteenth to the Twenty-first Century
RANJAN ROY
Beloit College
cambridge university press
Cambridge, New York, Melbourne, Madrid, Cape Town,
Singapore, São Paulo, Delhi, Tokyo, Mexico City
Cambridge University Press
32 Avenue of the Americas, New York, NY 10013-2473, USA
www.cambridge.org
Information on this title: www.cambridge.org/9780521114707
© Ranjan Roy 2011
This publication is in copyright. Subject to statutory exception
and to the provisions of relevant collective licensing agreements,
no reproduction of any part may take place without the written
permission of Cambridge University Press.
First published 2011
Printed in the United States of America
A catalog record for this publication is available from the British Library.
ISBN 978-0-521-11470-7 Hardback
Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or
third-party Internet Web sites referred to in this publication and does not guarantee that any content on such
Web sites is, or will remain, accurate or appropriate.
Contents
Preface page xvii

1 Power Series in Fifteenth-Century Kerala 1
1.1 Preliminary Remarks 1
1.2 Transformation of Series 4
1.3 Jyesthadeva on Sums of Powers 5
1.4 Arctangent Series in the Yuktibhasa 7
1.5 Derivation of the Sine Series in the Yuktibhasa 8
1.6 Continued Fractions 10
1.7 Exercises 12
1.8 Notes on the Literature 14
2 Sums of Powers of Integers 16
2.1 Preliminary Remarks 16
2.2 Johann Faulhaber and Sums of Powers 19
2.3 Jakob Bernoulli’s Polynomials 20
2.4 Proof of Bernoulli’s Formula 24
2.5 Exercises 25
2.6 Notes on the Literature 26
3 Infinite Product of Wallis 28
3.1 Preliminary Remarks 28
3.2 Wallis’s Infinite Product for π 32
3.3 Brouncker and Infinite Continued Fractions 33
3.4 Stieltjes: Probability Integral 36
3.5 Euler: Series and Continued Fractions 38
3.6 Euler: Products and Continued Fractions 40
3.7 Euler: Continued Fractions and Integrals 43
3.8 Sylvester: A Difference Equation and Euler’s Continued Fraction 45
3.9 Euler: Riccati’s Equation and Continued Fractions 46
3.10 Exercises 48
3.11 Notes on the Literature 50
v
vi Contents

4 The Binomial Theorem 51
4.1 Preliminary Remarks 51
4.2 Landen’s Derivation of the Binomial Theorem 57
4.3 Euler’s Proof for Rational Indices 58
4.4 Cauchy: Proof of the Binomial Theorem for Real Exponents 60
4.5 Abel’s Theorem on Continuity 62
4.6 Harkness and Morley’s Proof of the Binomial Theorem 66
4.7 Exercises 67
4.8 Notes on the Literature 69
5 The Rectification of Curves 71
5.1 Preliminary Remarks 71
5.2 Descartes’s Method of Finding the Normal 73
5.3 Hudde’s Rule for a Double Root 74
5.4 Van Heuraet’s Letter on Rectification 75
5.5 Newton’s Rectification of a Curve 76
5.6 Leibniz’s Derivation of the Arc Length 77
5.7 Exercises 78
5.8 Notes on the Literature 79
6 Inequalities 81
6.1 Preliminary Remarks 81
6.2 Harriot’s Proof of the Arithmetic and Geometric Means Inequality 87
6.3 Maclaurin’s Inequalities 88
6.4 Jensen’s Inequality 89
6.5 Reisz’s Proof of Minkowski’s Inequality 90
6.6 Exercises 91
6.7 Notes on the Literature 96
7 Geometric Calculus 97
7.1 Preliminary Remarks 97
7.2 Pascal’s Evaluation of


sinxdx 100
7.3 Gregory’s Evaluation of a Beta Integral 101
7.4 Gregory’s Evaluation of

secθdθ 104
7.5 Barrow’s Evaluation of

secθdθ 106
7.6 Barrow and the Integral

√
x
2
+a
2
dx 108
7.7 Barrow’s Proof of
d
dθ
tanθ =sec
2
θ 110
7.8 Barrow’s Product Rule for Derivatives 111
7.9 Barrow’s Fundamental Theorem of Calculus 114
7.10 Exercises 114
7.11 Notes on the Literature 118
8 The Calculus of Newton and Leibniz 120
8.1 Preliminary Remarks 120
8.2 Newton’s 1671 Calculus Text 123
8.3 Leibniz: Differential Calculus 126

Contents vii
8.4 Leibniz on the Catenary 129
8.5 Johann Bernoulli on the Catenary 131
8.6 Johann Bernoulli: The Brachistochrone 132
8.7 Newton’s Solution to the Brachistochrone 133
8.8 Newton on the Radius of Curvature 135
8.9 Johann Bernoulli on the Radius of Curvature 136
8.10 Exercises 137
8.11 Notes on the Literature 138
9 De Analysi per Aequationes Infinitas 140
9.1 Preliminary Remarks 140
9.2 Algebra of Infinite Series 142
9.3 Newton’s Polygon 145
9.4 Newton on Differential Equations 146
9.5 Newton’s Earliest Work on Series 147
9.6 De Moivre on Newton’s Formula for sinnθ 149
9.7 Stirling’s Proof of Newton’s Formula 150
9.8 Zolotarev: Lagrange Inversion with Remainder 152
9.9 Exercises 153
9.10 Notes on the Literature 156
10 Finite Differences: Interpolation and Quadrature 158
10.1 Preliminary Remarks 158
10.2 Newton: Divided Difference Interpolation 163
10.3 Gregory–Newton Interpolation Formula 165
10.4 Waring, Lagrange: Interpolation Formula 165
10.5 Cauchy, Jacobi: Lagrange Interpolation Formula 166
10.6 Newton on Approximate Quadrature 168
10.7 Hermite: Approximate Integration 170
10.8 Chebyshev on Numerical Integration 172
10.9 Exercises 173

10.10 Notes on the Literature 175
11 Series Transformation by Finite Differences 176
11.1 Preliminary Remarks 176
11.2 Newton’s Transformation 181
11.3 Montmort’s Transformation 182
11.4 Euler’s Transformation Formula 184
11.5 Stirling’s Transformation Formulas 187
11.6 Nicole’s Examples of Sums 190
11.7 Stirling Numbers 191
11.8 Lagrange’s Proof of Wilson’s Theorem 194
11.9 Taylor’s Summation by Parts 195
11.10 Exercises 196
11.11 Notes on the Literature 199
viii Contents
12 The Taylor Series 200
12.1 Preliminary Remarks 200
12.2 Gregory’s Discovery of the Taylor Series 206
12.3 Newton: An Iterated Integral as a Single Integral 209
12.4 Bernoulli and Leibniz: A Form of the Taylor Series 210
12.5 Taylor and Euler on the Taylor Series 211
12.6 Lacroix on d’Alembert’s Derivation of the Remainder 212
12.7 Lagrange’s Derivation of the Remainder Term 213
12.8 Laplace’s Derivation of the Remainder Term 215
12.9 Cauchy on Taylor’s Formula and l’Hôpital’s Rule 216
12.10 Cauchy: The Intermediate Value Theorem 218
12.11 Exercises 219
12.12 Notes on the Literature 220
13 Integration of Rational Functions 222
13.1 Preliminary Remarks 222
13.2 Newton’s 1666 Basic Integrals 228

13.3 Newton’s Factorization of x
n
±1 230
13.4 Cotes and de Moivre’s Factorizations 231
13.5 Euler: Integration of Rational Functions 233
13.6 Euler’s Generalization of His Earlier Work 234
13.7 Hermite’s Rational Part Algorithm 237
13.8 Johann Bernoulli: Integration of
√
ax
2
+bx +c 238
13.9 Exercises 239
13.10 Notes on the Literature 243
14 Difference Equations 245
14.1 Preliminary Remarks 245
14.2 De Moivre on Recurrent Series 247
14.3 Stirling’s Method of Ultimate Relations 250
14.4 Daniel Bernoulli on Difference Equations 252
14.5 Lagrange: Nonhomogeneous Equations 254
14.6 Laplace: Nonhomogeneous Equations 257
14.7 Exercises 258
14.8 Notes on the Literature 259
15 Differential Equations 260
15.1 Preliminary Remarks 260
15.2 Leibniz: Equations and Series 268
15.3 Newton on Separation of Variables 270
15.4 Johann Bernoulli’s Solution of a First-Order Equation 271
15.5 Euler on General Linear Equations with Constant Coefficients 272
15.6 Euler: Nonhomogeneous Equations 274

15.7 Lagrange’s Use of the Adjoint 276
15.8 Jakob Bernoulli and Riccati’s Equation 278
15.9 Riccati’s Equation 278
Contents ix
15.10 Singular Solutions 279
15.11 Mukhopadhyay on Monge’s Equation 283
15.12 Exercises 285
15.13 Notes on the Literature 287
16 Series and Products for Elementary Functions 289
16.1 Preliminary Remarks 289
16.2 Euler: Series for Elementary Functions 292
16.3 Euler: Products for Trigonometric Functions 293
16.4 Euler’s Finite Product for sinnx 294
16.5 Cauchy’s Derivation of the Product Formulas 295
16.6 Euler and Niklaus I Bernoulli: Partial Fractions Expansions of
Trigonometric Functions 298
16.7 Euler: Dilogarithm 301
16.8 Landen’s Evaluation of ζ(2) 302
16.9 Spence: Two-Variable Dilogarithm Formula 304
16.10 Exercises 306
16.11 Notes on the Literature 310
17 Solution of Equations by Radicals 311
17.1 Preliminary Remarks 311
17.2 Viète’s Trigonometric Solution of the Cubic 316
17.3 Descartes’s Solution of the Quartic 318
17.4 Euler’s Solution of a Quartic 319
17.5 Gauss: Cyclotomy, Lagrange Resolvents, and Gauss Sums 320
17.6 Kronecker: Irreducibility of the Cyclotomic Polynomial 324
17.7 Exercises 325
17.8 Notes on the Literature 325

18 Symmetric Functions 326
18.1 Preliminary Remarks 326
18.2 Euler’s Proofs of Newton’s Rule 331
18.3 Maclaurin’s Proof of Newton’s Rule 332
18.4 Waring’s Power Sum Formula 334
18.5 Gauss’s Fundamental Theorem of Symmetric Functions 334
18.6 Cauchy: Fundamental Theorem of Symmetric Functions 335
18.7 Cauchy: Elementary Symmetric Functions as Rational
Functions of Odd Power Sums 336
18.8 Laguerre and Pólya on Symmetric Functions 337
18.9 MacMahon’s Generalization of Waring’s Formula 340
18.10 Exercises 343
18.11 Notes on the Literature 344
19 Calculus of Several Variables 346
19.1 Preliminary Remarks 346
19.2 Homogeneous Functions 351
19.3 Cauchy: Taylor Series in Several Variables 352
x Contents
19.4 Clairaut: Exact Differentials and Line Integrals 354
19.5 Euler: Double Integrals 356
19.6 Lagrange’s Change of Variables Formula 358
19.7 Green’s Integral Identities 359
19.8 Riemann’s Proof of Green’s Formula 361
19.9 Stokes’s Theorem 362
19.10 Exercises 365
19.11 Notes on the Literature 365
20 Algebraic Analysis: The Calculus of Operations 367
20.1 Preliminary Remarks 367
20.2 Lagrange’s Extension of the Euler–Maclaurin Formula 375
20.3 Français’s Method of Solving Differential Equations 379

20.4 Herschel: Calculus of Finite Differences 380
20.5 Murphy’s Theory of Analytical Operations 382
20.6 Duncan Gregory’s Operational Calculus 384
20.7 Boole’s Operational Calculus 387
20.8 Jacobi and the Symbolic Method 390
20.9 Cartier: Gregory’s Proof of Leibniz’s Rule 392
20.10 Hamilton’s Algebra of Complex Numbers and Quaternions 393
20.11 Exercises 397
20.12 Notes on the Literature 398
21 Fourier Series 400
21.1 Preliminary Remarks 400
21.2 Euler: Trigonometric Expansion of a Function 406
21.3 Lagrange on the Longitudinal Motion of the Loaded
Elastic String 407
21.4 Euler on Fourier Series 410
21.5 Fourier: Linear Equations in Infinitely Many Unknowns 412
21.6 Dirichlet’s Proof of Fourier’s Theorem 417
21.7 Dirichlet: On the Evaluation of Gauss Sums 421
21.8 Exercises 424
21.9 Notes on the Literature 425
22 Trigonometric Series after 1830 427
22.1 Preliminary Remarks 427
22.2 The Riemann Integral 429
22.3 Smith: Revision of Riemann and Discovery of the Cantor Set 431
22.4 Riemann’s Theorems on Trigonometric Series 432
22.5 The Riemann–Lebesgue Lemma 436
22.6 Schwarz’s Lemma on Generalized Derivatives 436
22.7 Cantor’s Uniqueness Theorem 437
22.8 Exercises 439
22.9 Notes on the Literature 443

Contents xi
23 The Gamma Function 444
23.1 Preliminary Remarks 444
23.2 Stirling: (1/2) by Newton–Bessel Interpolation 450
23.3 Euler’s Evaluation of the Beta Integral 453
23.4 Gauss’s Theory of the Gamma Function 457
23.5 Poisson, Jacobi, and Dirichlet: Beta Integrals 460
23.6 Bohr, Mollerup, and Artin on the Gamma Function 462
23.7 Kummer’s Fourier Series for ln (x) 465
23.8 Exercises 467
23.9 Notes on the Literature 474
24 The Asymptotic Series for ln(x) 476
24.1 Preliminary Remarks 476
24.2 De Moivre’s Asymptotic Series 481
24.3 Stirling’s Asymptotic Series 483
24.4 Binet’s Integrals for ln (x) 486
24.5 Cauchy’s Proof of the Asymptotic Character of de Moivre’s Series 488
24.6 Exercises 489
24.7 Notes on the Literature 493
25 The Euler–Maclaurin Summation Formula 494
25.1 Preliminary Remarks 494
25.2 Euler on the Euler–Maclaurin Formula 499
25.3 Maclaurin’s Derivation of the Euler–Maclaurin Formula 501
25.4 Poisson’s Remainder Term 503
25.5 Jacobi’s Remainder Term 505
25.6 Euler on the Fourier Expansions of Bernoulli Polynomials 507
25.7 Abel’s Derivation of the Plana–Abel Formula 508
25.8 Exercises 509
25.9 Notes on the Literature 513
26 L-Series 515

26.1 Preliminary Remarks 515
26.2 Euler’s First Evaluation of

1/n
2k
521
26.3 Euler: Bernoulli Numbers and

1/n
2k
522
26.4 Euler’s Evaluation of Some L-Series Values by Partial Fractions 524
26.5 Euler’s Evaluation of

1/n
2
by Integration 525
26.6 N. Bernoulli’s Evaluation of

1/(2n +1)
2
527
26.7 Euler and Goldbach: Double Zeta Values 528
26.8 Dirichlet’s Summation of L(1,χ) 532
26.9 Eisenstein’s Proof of the Functional Equation 535
26.10 Riemann’s Derivations of the Functional Equation 536
26.11 Euler’s Product for

1/n
s

539
26.12 Dirichlet Characters 540
26.13 Exercises 542
26.14 Notes on the Literature 545
xii Contents
27 The Hypergeometric Series 547
27.1 Preliminary Remarks 547
27.2 Euler’s Derivation of the Hypergeometric Equation 555
27.3 Pfaff’s Derivation of the
3
F
2
Identity 556
27.4 Gauss’s Contiguous Relations and Summation Formula 557
27.5 Gauss’s Proof of the Convergence of F(a, b,c,x)
for c −a −b>0 559
27.6 Gauss’s Continued Fraction 560
27.7 Gauss: Transformations of Hypergeometric Functions 561
27.8 Kummer’s 1836 Paper on Hypergeometric Series 564
27.9 Jacobi’s Solution by Definite Integrals 565
27.10 Riemann’s Theory of Hypergeometric Functions 567
27.11 Exercises 569
27.12 Notes on the Literature 572
28 Orthogonal Polynomials 574
28.1 Preliminary Remarks 574
28.2 Legendre’s Proof of the Orthogonality of His Polynomials 578
28.3 Gauss on Numerical Integration 579
28.4 Jacobi’s Commentary on Gauss 582
28.5 Murphy and Ivory: The Rodrigues Formula 583
28.6 Liouville’s Proof of the Rodrigues Formula 585

28.7 The Jacobi Polynomials 587
28.8 Chebyshev: Discrete Orthogonal Polynomials 590
28.9 Chebyshev and Orthogonal Matrices 594
28.10 Chebyshev’s Discrete Legendre and Jacobi Polynomials 594
28.11 Exercises 596
28.12 Notes on the Literature 597
29 q-Series 599
29.1 Preliminary Remarks 599
29.2 Jakob Bernoulli’s Theta Series 605
29.3 Euler’s q-series Identities 605
29.4 Euler’s Pentagonal Number Theorem 606
29.5 Gauss: Triangular and Square Numbers Theorem 608
29.6 Gauss Polynomials and Gauss Sums 611
29.7 Gauss’s q-Binomial Theorem and the Triple Product Identity 615
29.8 Jacobi: Triple Product Identity 617
29.9 Eisenstein: q-Binomial Theorem 618
29.10 Jacobi’s q-Series Identity 619
29.11 Cauchy and Ramanujan: The Extension of the Triple
Product 621
29.12 Rodrigues and MacMahon: Combinatorics 622
29.13 Exercises 623
29.14 Notes on the Literature 625
Contents xiii
30 Partitions 627
30.1 Preliminary Remarks 627
30.2 Sylvester on Partitions 638
30.3 Cayley: Sylvester’s Formula 642
30.4 Ramanujan: Rogers–Ramanujan Identities 644
30.5 Ramanujan’s Congruence Properties of Partitions 646
30.6 Exercises 649

30.7 Notes on the Literature 651
31 q-Series and q-Orthogonal Polynomials 653
31.1 Preliminary Remarks 653
31.2 Heine’s Transformation 661
31.3 Rogers: Threefold Symmetry 662
31.4 Rogers: Rogers–Ramanujan Identities 665
31.5 Rogers: Third Memoir 670
31.6 Rogers–Szeg
˝
o Polynomials 671
31.7 Feldheim and Lanzewizky: Orthogonality of q-Ultraspherical
Polynomials 673
31.8 Exercises 677
31.9 Notes on the Literature 679
32 Primes in Arithmetic Progressions 680
32.1 Preliminary Remarks 680
32.2 Euler: Sum of Prime Reciprocals 682
32.3 Dirichlet: Infinitude of Primes in an Arithmetic Progression 683
32.4 Class Number and L
χ
(1) 686
32.5 De la Vallée Poussin’s Complex Analytic Proof of L
χ
(1) = 0 688
32.6 Gelfond and Linnik: Proof of L
χ
(1) = 0 689
32.7 Monsky’s Proof That L
χ
(1) = 0 691

32.8 Exercises 692
32.9 Notes on the Literature 694
33 Distribution of Primes: Early Results 695
33.1 Preliminary Remarks 695
33.2 Chebyshev on Legendre’s Formula 701
33.3 Chebyshev’s Proof of Bertrand’s Conjecture 705
33.4 De Polignac’s Evaluation of

p≤x
lnp
p
710
33.5 Mertens’s Evaluation of

p≤x

1 −
1
p

−1
710
33.6 Riemann’s Formula for π(x) 714
33.7 Exercises 717
33.8 Notes on the Literature 719
34 Invariant Theory: Cayley and Sylvester 720
34.1 Preliminary Remarks 720
34.2 Boole’s Derivation of an Invariant 729
xiv Contents
34.3 Differential Operators of Cayley and Sylvester 733

34.4 Cayley’s Generating Function for the Number of Invariants 736
34.5 Sylvester’s Fundamental Theorem of Invariant Theory 740
34.6 Hilbert’s Finite Basis Theorem 743
34.7 Hilbert’s Nullstellensatz 746
34.8 Exercises 746
34.9 Notes on the Literature 747
35 Summability 749
35.1 Preliminary Remarks 749
35.2 Fejér: Summability of Fourier Series 760
35.3 Karamata’s Proof of the Hardy–Littlewood Theorem 763
35.4 Wiener’s Proof of Littlewood’s Theorem 764
35.5 Hardy and Littlewood: The Prime Number Theorem 766
35.6 Wiener’s Proof of the PNT 768
35.7 Kac’s Proof of Wiener’s Theorem 771
35.8 Gelfand: Normed Rings 772
35.9 Exercises 775
35.10 Notes on the Literature 777
36 Elliptic Functions: Eighteenth Century 778
36.1 Preliminary Remarks 778
36.2 Fagnano Divides the Lemniscate 786
36.3 Euler: Addition Formula 790
36.4 Cayley on Landen’s Transformation 791
36.5 Lagrange, Gauss, Ivory on the agM 794
36.6 Remarks on Gauss and Elliptic Functions 800
36.7 Exercises 811
36.8 Notes on the Literature 813
37 Elliptic Functions: Nineteenth Century 816
37.1 Preliminary Remarks 816
37.2 Abel: Elliptic Functions 821
37.3 Abel: Infinite Products 823

37.4 Abel: Division of Elliptic Functions and Algebraic Equations 826
37.5 Abel: Division of the Lemniscate 830
37.6 Jacobi’s Elliptic Functions 832
37.7 Jacobi: Cubic and Quintic Transformations 834
37.8 Jacobi’s Transcendental Theory of Transformations 839
37.9 Jacobi: Infinite Products for Elliptic Functions 844
37.10 Jacobi: Sums of Squares 847
37.11 Cauchy: Theta Transformations and Gauss Sums 849
37.12 Eisenstein: Reciprocity Laws 852
37.13 Liouville’s Theory of Elliptic Functions 858
37.14 Exercises 863
37.15 Notes on the Literature 865
Contents xv
38 Irrational and Transcendental Numbers 867
38.1 Preliminary Remarks 867
38.2 Liouville Numbers 878
38.3 Hermite’s Proof of the Transcendence of e 880
38.4 Hilbert’s Proof of the Transcendence of e 884
38.5 Exercises 885
38.6 Notes on the Literature 886
39 Value Distribution Theory 887
39.1 Preliminary Remarks 887
39.2 Jacobi on Jensen’s Formula 892
39.3 Jensen’s Proof 894
39.4 Bäcklund Proof of Jensen’s Formula 895
39.5 R. Nevanlinna’s Proof of the Poisson–Jensen Formula 896
39.6 Nevanlinna’s First Fundamental Theorem 898
39.7 Nevanlinna’s Factorization of a Meromorphic Function 901
39.8 Picard’s Theorem 902
39.9 Borel’s Theorem 902

39.10 Nevanlinna’s Second Fundamental Theorem 903
39.11 Exercises 905
39.12 Notes on the Literature 906
40 Univalent Functions 907
40.1 Preliminary Remarks 907
40.2 Gronwall: Area Inequalities 914
40.3 Bieberbach’s Conjecture 916
40.4 Littlewood: |a
n
|≤en 917
40.5 Littlewood and Paley on Odd Univalent Functions 918
40.6 Karl Löwner and the Parametric Method 920
40.7 De Branges: Proof of Bieberbach’s Conjecture 923
40.8 Exercises 927
40.9 Notes on the Literature 928
41 Finite Fields 929
41.1 Preliminary Remarks 929
41.2 Euler’s Proof of Fermat’s Little Theorem 932
41.3 Gauss’s Proof that
Z
×
p
Is Cyclic 932
41.4 Gauss on Irreducible Polynomials Modulo a Prime 933
41.5 Galois on Finite Fields 936
41.6 Dedekind’s Formula 939
41.7 Exercises 940
41.8 Notes on the Literature 941
References 943
Index 959

Preface
But this is something very important; one can render our youthful students no greater
service than to give them suitable guidance, so that the advances in science become
known to them through a study of the sources. – Weierstrass to Casorati, December 21,
1868
The development of infinite series and products marked the beginning of the modern
mathematical era. In his Arithmetica Infinitorum of 1656, Wallis made groundbreak-
ing discoveries in the use of such products and continued fractions. This work had a
tremendous catalytic effect on the young Newton, leading him to the discovery of the
binomial theorem for noninteger exponents. Newton explained in his De Methodis that
the central pillar of his work in algebra and calculus was the powerful new method of
infinite series. In letters written in 1670, James Gregory presented his discovery of sev-
eral infinite series, most probably by means of finite difference interpolation formulas.
Illustrating the very significant connections between series and finite difference meth-
ods, in the 1670s Newton made use of such methods to transform slowly convergent
or even divergent series into rapidly convergent series, though he did not publish his
results. Illustrating theimportance of this approach, Montmort and Euler soon used new
arguments to rediscover it. Newton further wrote in the De Methodis that he conceived
of infinite series as analogues of infinite decimals, so that the four arithmetical opera-
tions and root extraction could be carried over to apply to variables. Thus, he applied
infinite series to discover the inverse function and implicit function theorems. Newton
concentrated largely on analysis and mathematical physics; Euler’s prodigious intellect
broadened Newton’s conception to apply infinite series and products to number theory,
algebra, and combinatorics; this legacy continues unabated even today.
Infinite series have numerous manifestations, including power series, trigonometric
series, q-series, and Dirichlet series. Their scope and power are evident in their piv-
otal role in many areas of mathematics, including algebra, analysis, combinatorics, and
number theory. As such, infinite series and products provide access to many mathe-
matical questions and insights. For example, Maclaurin, Euler, and MacMahon studied

symmetric functions using infinite series; Euler, Dirichlet, Chebyshev, and Riemann
employed products and series to get deep insight into the distribution of primes. Gauss
xvii
xviii Preface
employed q-series to prove the law of quadratic reciprocity and Jacobi applied the
triple product identity, also discovered by Gauss, to determine the number of represen-
tations of integers as sums of squares. Moreover, the correspondence between Daniel
Bernoulli and Goldbach in the 1720s introduced the problem of determining whether a
given series of rational numbers was irrational or transcendental. The 1843 publication
of their letters prompted Liouville to lay the foundations of the theory of transcendental
numbers.
The detailed table of contents at the beginning of this book may prove even more
useful than the index in locating particular topics or questions.The preliminary remarks
in each chapter provide some background on the origins and motivations of the ideas
discussed in the subsequent, more detailed, and substantial sections of the chapter.
The exercises following these sections offer references so that the reader may perhaps
consult the original sources with a specific focus in mind. Most works cited in the notes
at the end of each chapter should be readily accessible, especially since the number of
books and papers online is increasing steadily.
Mathematics teachers and students may discover that the old sources, such as
Simpson’s books on algebra and calculus, Euler’s Introductio, or the correspondence
of Euler and Goldbach and the Bernoullis, are fruitful resources for calculus projects or
undergraduate or graduate seminar topics. Since early mathematicians often omitted to
mention the conditions under which their results would hold, analysis students could
find it very instructive to work out the range of validity of those results. For example,
Landen’s formula for the dilogarithm, while very insightful and significant, is incorrect
for a range of values, even where the series converge. At an advanced level, important
research has arisen out of a study of old works. Indeed, by studying Descartes and
Newton, Laguerre revived a subject others had abandoned for two hundred years and
did his excellent work in numerical solutions of algebraic equations and extensions

of the rule of signs. Again, André Weil recounted in his 1972 Ritt lectures on number
theory that he arrived at the Weil conjectures through a study of Gauss’s two papers on
biquadratic residues.
It is edifying and a lot of fun to read the noteworthy works of long ago; this is
common practice in literature and is equally appropriate and beneficial in mathematics.
For example, a calculus student might enjoy and learn from Cotes’s 1714 paper on
logarithms or Maria Agnesi’s 1748 treatment of the same topic in her work on analysis.
At a more advanced level, Euler gave not just one or two but at least eight derivations
of his famous formula

1/n
2
=π
2
/6. Reading these may serve to enlighten us on the
variety of approaches to the perennial problem of summing series, though most of these
approaches are not mentioned in textbooks. Students of literature routinely learn from
and enjoy reading the words of, say,Austen, Hawthorne, Turgenev, or Shakespeare. We
may likewise deepen our understanding and enjoyment of mathematics by reading and
rereading the original works of mathematicians such as Barrow, Laplace, Chebyshev,
or Newton. It might prove rewarding if mathematicians and students of mathematics
were to make such reading a regular practice. In the introduction to his Development
of Mathematics in the 19th Century, Felix Klein wrote, “Thus, it is impossible to grasp
even one mathematical concept without having assimilated all the concepts which led
up to its creation, and their connections.”
Preface xix
Wherever practical, I have tried to present a mathematician’s own notational meth-
ods. Seeing an argument in its original form is often instructive and can give us insight
into its motivations and underlying rationale. Because of the numerous notations for
logarithms, for simplicity I have denoted the logarithm of a real value by the familiar

ln; in the case of complex or non-e-based logarithms, I have used log.
I am indebted to many persons who helped me in writing this book. I would first like
to thank my wife, Gretchen Roy, for her invaluable assistance in editing and preparing
the manuscript. I am grateful to Kalyan for his beautiful cover art. I thank my col-
leagues: Paul Campbell for his expert and generous assistance with the indexes and
typesetting and Bruce Atwood for so cheerfully and accurately preparing the figures as
they now appear. I am grateful to Ashish Thapa for his skillful typesetting and figure
construction. Many thanks to Doreen Dalman, who typeset the majority of the book
and did valuable troubleshooting. I am obliged to Paul Campbell and David Heesen
for their meticulous work on the bibliography. I benefited from the input of those who
read preliminary drafts of some chapters: Richard Askey, George Andrews, Lonnie
Fairchild, Atar Mittal, Yu Shun, and Phil Straffin. I was fortunate to receive assistance
from very capable librarians: Cindy Cooley and Chris Nelson at Beloit College, Travis
Warwick at the Kleene Mathematics Library at the University of Wisconsin, the effi-
cient librarians at the University Library in Cambridge, and the kind librarians at St.
Andrews University Library. A. W. F. Edwards, of Gonville and Caius College, also
gave me helpful guidance. I am grateful for financial and other assistance from Beloit
College; thanks to John Burris, Lynn Franken, and Ann Davies for their encourage-
ment and support. Heartfelt gratitude goes to Maitreyi Lagunas, Margaret Carey, Mihir
Banerjee, Sahib RamMandan, and Ramendra Bose. Finally, I am deeply indebted to my
parents for their intellectual, emotional, and practical support of my efforts to become
a mathematician. I dedicate this book to their memory.

1
Power Series in Fifteenth-Century Kerala
1.1 Preliminary Remarks
The Indian astronomer and mathematician Madhava (c. 1340–c. 1425) discovered
infinite power series about two and a half centuries before Newton rediscovered them
in the 1660s. Madhava’s work may have been motivated by his studies in astronomy,
since he concentrated mainly on the trigonometric functions. There appears to be no

connection between Madhava’s school and that of Newton and other European math-
ematicians. In spite of this, the Keralese and European mathematicians shared some
similar methods and results. Both were fascinated with transformation of series, though
here they used very different methods.
The mathematician-astronomers of medieval Kerala lived, worked, and taught in
large family compounds called illams. Madhava, believed to have been the founder
of the school, worked in the Bakulavihara illam in the town of Sangamagrama, a few
miles north of Cochin. He was an Emprantiri Brahmin, then considered socially inferior
to the dominant Namputiri (or Nambudri) Brahmin. This position does not appear to
have curtailed his teaching activities; his most distinguished pupil was Paramesvara, a
Namputiri Brahmin. No mathematical worksof Madhava havebeen found,though three
of his short treatises on astronomy are extant. The most important of these describes
how to accurately determine the position of the moon at any time of the day. Other
surviving mathematical works of the Kerala school attribute many very significant
results to Madhava. Although his algebraic notation was almost primitive, Madhava’s
mathematical skill allowed him to carry out highly original and difficult research.
Paramesvara (c.1380–c.1460), Madhava’s pupil, was from Asvattagram, about
thirty-five milesnortheast ofMadhava’s hometown. Hebelonged totheVatasreni illam,
a famous center for astronomy and mathematics. He made a series of observations of
the eclipses of the sun and the moon between 1395 and 1432 and composed several
astronomical texts, the last of which was written in the 1450s, near the end of his life.
Sankara Variyar attributed to Paramesvara a formula for the radius of a circle in terms of
the sides of an inscribed quadrilateral. Paramesvara’s son, Damodara, was the teacher
of Jyesthadeva (c. 1500–c. 1570) whose works survive and give us all the surviving
proofs of this school. Damodara was also the teacher of Nilakantha (c. 1450–c. 1550)
1
2 Power Series in Fifteenth-Century Kerala
who composed the famous treatise called the Tantrasangraha (c. 1500), a digest of the
mathematical and astronomical knowledge of his time. His works allow us determine
his approximate dates since in his Aryabhatyabhasya, Nilakantha refers to his observa-

tion of solar eclipses in 1467 and 1501. Nilakanthamade several efforts to establish new
parameters for the mean motions of the planets and vigorously defended the necessity
of continually correcting astronomical parameters on the basis of observation. Sankara
Variyar (c. 1500–1560) was his student.
The surviving texts containing results on infinite series are Nilakantha’s Tantrasan-
graha, a commentary on it by Sankara Variyar called Yuktidipika, the Yuktibhasa by
Jyesthadeva and the Kriyakramakari, started by Variyar and completed by his student
Mahisamangalam Narayana.All theseworks are inSanskrit exceptthe Yuktibhasa, writ-
ten in Malayalam, the language of Kerala. These works provide a summary of major
results on series discovered by these original mathematicians of the indistinct past:
A. Series expansions for arctangent, sine, and cosine:
1. θ =tan θ −
tan
3
θ
3
+
tan
5
θ
5
−···,
2. sin θ =θ −
θ
3
3!
+
θ
5
5!

−···,
3. cos θ =1 −
θ
2
2!
+
θ
4
4!
−···,
4. sin
2
θ =θ
2
−
θ
4
(2
2
−2/2)
+
θ
6
(2
2
−2/2)(3
2
−3/2)
−
θ

8
(2
2
−2/2)(3
2
−3/2)(4
2
−4/2)
+···.
In the proofs of these formulas, the range of θ for the first series was 0 ≤θ ≤π/4
and for the second and third was 0 ≤θ ≤ π/2. Although the series for sine and
cosine converge for allreal values, theconcept of periodicityof the trigonometric
functions was discovered much later.
B. Series for π:
1.
π
4
≈1 −
1
3
+
1
5
−···∓
1
n
±f
i
(n +1), i =1, 2,3, where
f

1
(n) = 1/(2n), f
2
(n) = n/(2(n
2
+1)),
and
f
3
(n) = (n
2
+4)/(2n(n
2
+5));
2.
π
4
=
3
4
+
1
3
3
−3
−
1
5
3
−5

+
1
7
3
−7
−···;
3.
π
4
=
4
1
5
+4·1
−
4
3
5
+4·3
+
4
5
5
+4·5
−···;
4.
π
2
√
3

=1 −
1
3·3
+
1
5·3
2
−
1
7·3
3
+···;
5.
π
6
=
1
2
+
1
(2·2
2
−1)
2
−2
2
+
1
(2·4
2

−1)
2
−4
2
+
1
(2·6
2
−1)
2
−6
2
+···;
6.
π−2
4
≈
1
2
2
−1
−
1
4
2
−1
+
1
6
2

−1
−···∓
1
n
2
−1
±
1
2
(
(n+1)
2
+2
)
.
These results were stated in verse form. Thus, the series for sine was described:
The arc is to be repeatedly multiplied by the square of itself and is to be divided [in order] by the
square of each even number increased by itself and multiplied by the square of the radius. The
arc and the terms obtained by these repeated operations are to be placed in sequence in a column,
1.1 Preliminary Remarks 3
and any last term is to be subtracted from the next above, the remainder from the term then next
above, and so on, to obtain the jya (sine) of the arc.
So if r is the radius and s the arc, then the successive terms of the repeated operations
mentioned in the description are given by
s ·
s
2
(2
2
+2)r

2
,s·
s
2
(2
2
+2)r
2
·
s
2
(4
2
+4)r
2
,
and the equation is
y =s −s ·
s
2
(2
2
+2)r
2
+s ·
s
2
(2
2
+2)r

2
·
s
2
(4
2
+4)r
2
−···
where y = r sin(s/r). Nilakantha’s Aryabhatiyabhasya attributes the sine series to
Madhava. The Kriyakramakari attributes to Madhava the first two cases of B.1, the
arctangent series, and series B.4; note that B.4 can be derived from the arctangent
by taking θ = π/6. The extant manuscripts do not appear to attribute the other series
to a particular person. The Yuktidipika gives series B.6, including the remainder; it
is possible that this series is due to Sankara Variyar, the author of the work. We can
safely conclude that the power series for arctangent, sine, and cosine were obtained by
Madhava; he is, thus, the first person to express the trigonometric functions as series.
In the 1660s, Newton rediscovered the sine and cosine series; in 1671, James Gregory
rediscovered the series for arctangent.
The series for sin
2
θ follows directly from the series for cos θ by an application of
the double angle formula, sin
2
θ =
1
2
(1 −cos2θ). The series for π/4 (B.1) has several
points of interest. When n →∞, it is simply the series discovered by Leibniz in 1673.
However, this series is not useful for computational purposes because it converges

extremely slowly. To make it more effective in this respect, the Madhava school added
a rational approximation for the remainder after n terms. They did not explain how they
arrived at the three expressions f
i
(n) in B.1. However, if we set
π
4
=1 −
1
3
+
1
5
−···∓
1
n
±f (n), (1.1)
then the remainder f (n) has the continued fraction expansion
f (n) =
1
2
·
1
n+
1
2
n+
2
2
n+

3
2
n+
···, (1.2)
when f (n) is assumed to satisfy the functional relation
f(n+1) +f(n−1) =
1
n
. (1.3)
The first three convergents of this continued fraction are
1
2n
=f
1
(n),
n
2(n
2
+1)
=f
2
(n), and
1
2
n
2
+4
n(n
2
+5)

=f
3
(n). (1.4)