View source for Biography:Pierre de Fermat

{{short description|French mathematician and lawyer}}
{{Infobox scientist
| name        = Pierre de Fermat
| image       = Pierre de Fermat.jpg
| caption     = Pierre de Fermat, 17th century painting by unknown author
| birth_date  = 1607?{{efn|name=birth}}
| birth_place = Beaumont-de-Lomagne, [[History:Kingdom of France|France]]
| death_date  = {{death date|1665|01|12|df=y}}<br />(aged 57)
| death_place = Castres, [[History:Kingdom of France|France]]
| education   = [[Organization:University of Orléans|University of Orléans]] (LL.B., 1626)
| field       = [[Mathematics]] and [[Philosophy:Law|law]]
| known_for   = Contributions to [[Number theory|number theory]], [[Analytic geometry|analytic geometry]], [[Probability theory|probability theory]]<br />[[Folium of Descartes]]<br />[[Fermat's principle]]<br />[[Fermat's little theorem]]<br />[[Fermat's Last Theorem]]<br />[[Adequality]]<br />Fermat's "[[Difference quotient|difference quotient]]" method<ref>Benson, Donald C. (2003). ''A Smoother Pebble: Mathematical Explorations'', Oxford University Press, p. 176.</ref><br />(See full list) 
}}

'''Pierre de Fermat''' ({{IPA-fr|pjɛʁ də fɛʁma|lang}}; between 31 October and 6 December 1607{{efn|name=birth|Most sources give Fermat's birth year as 1601; however, recent research suggests this was the year a half-brother called Piere was born and, working backwards from the stated age at death, gives 1607 as his birth year.<ref name="birthyear"/> Piere died before Pierre was born.}} – 12 January 1665) was a French [[Biography:Mathematician|mathematician]] who is given credit for early developments that led to infinitesimal calculus, including his technique of [[Adequality|adequality]]. In particular, he is recognized for his discovery of an original method of finding the greatest and the smallest ordinates of curved lines, which is analogous to that of [[Differential calculus|differential calculus]], then unknown, and his research into [[Number theory|number theory]]. He made notable contributions to [[Analytic geometry|analytic geometry]], [[Probability|probability]], and [[Physics:Optics|optics]]. He is best known for his [[Fermat's principle]] for light propagation and his [[Fermat's Last Theorem]] in [[Number theory|number theory]], which he described in a note at the margin of a copy of [[Biography:Diophantus|Diophantus]]' ''Arithmetica''. He was also a lawyer<ref>[https://books.google.com/books?id=59ITUOLbVkoC&q=%22French+lawyer&pg=PA101 W.E. Burns, The Scientific Revolution: An Encyclopedia, ABC-CLIO, 2001, p. 101]</ref> at the ''Parlement'' of Toulouse, {{wipe|France}}.

==Biography==
[[File:Pierre de Fermat3.jpg|thumb|right|upright|Pierre de Fermat, 17th century painting by {{ill|Rolland Lefebvre|fr}}]]
Fermat was born in 1607{{efn|name=birth}} in Beaumont-de-Lomagne, France—the late 15th-century mansion where Fermat was born is now a museum. He was from Gascony, where his father, Dominique Fermat, was a wealthy leather merchant and served three one-year terms as one of the four consuls of Beaumont-de-Lomagne. His mother was Claire de Long.<ref name="birthyear">{{Cite web|url=https://www.maa.org/press/periodicals/convergence/when-was-pierre-de-fermat-born|title=When Was Pierre de Fermat Born? {{!}} Mathematical Association of America|website=www.maa.org|access-date=2017-07-09}}</ref> Pierre had one brother and two sisters and was almost certainly brought up in the town of his birth.{{citation needed|date=April 2021}}

He attended the [[Organization:University of Orléans|University of Orléans]] from 1623 and received a bachelor in civil law in 1626, before moving to [[Earth:Bordeaux|Bordeaux]]. In Bordeaux, he began his first serious mathematical researches, and in 1629 he gave a copy of his restoration of [[Biography:Apollonius of Perga|Apollonius]]'s ''[[Biography:Apollonius of Perga#De Locis Planis|De Locis Planis]]'' to one of the mathematicians there. Certainly, in Bordeaux he was in contact with Beaugrand and during this time he produced important work on [[Maxima and minima|maxima and minima]] which he gave to Étienne d'Espagnet who clearly shared mathematical interests with Fermat. There he became much influenced by the work of [[Biography:François Viète|François Viète]].<ref>{{Cite web |last=Chad |date=2013-12-26 |title=Pierre de Fermat Biography - Life of French Mathematician |url=https://totallyhistory.com/pierre-de-fermat/ |access-date=2023-02-22 |website=Totally History |language=en-US}}</ref>

In 1630, he bought the office of a councilor at the Parlement de Toulouse, one of the High Courts of Judicature in France, and was sworn in by the Grand Chambre in May 1631. He held this office for the rest of his life. Fermat thereby became entitled to change his name from Pierre Fermat to Pierre de Fermat. On 1 June 1631, Fermat married Louise de Long, a fourth cousin of his mother Claire de Fermat (née de Long). The Fermats had eight children, five of whom survived to adulthood: Clément-Samuel, Jean, Claire, Catherine, and Louise.<ref>{{cite web | title=Fermat, Pierre De | url=https://www.encyclopedia.com/people/science-and-technology/mathematics-biographies/pierre-de-fermat | website=www.encyclopedia.com | access-date=2020-01-25 }}</ref><ref>{{cite web | last1 = Davidson | first1 = Michael W. | title=Pioneers in Optics: Pierre de Fermat | url=https://micro.magnet.fsu.edu/optics/timeline/people/fermat.html | website=micro.magnet.fsu.edu | access-date=2020-01-25 }}</ref><ref>{{cite web | title=Pierre de Fermat's Biography | url=https://www.famousscientists.org/pierre-de-fermat/ | website=www.famousscientists.org | access-date=2020-01-25 }}</ref>

Fluent in six languages ([[Social:French language|French]], [[Social:Latin|Latin]], Occitan, classical Greek, [[Social:Italian language|Italian]] and [[Social:Spanish language|Spanish]]), Fermat was praised for his written verse in several languages and his advice was eagerly sought regarding the emendation of Greek texts. He communicated most of his work in letters to friends, often with little or no proof of his theorems. In some of these letters to his friends, he explored many of the fundamental ideas of calculus before [[Biography:Isaac Newton|Newton]] or [[Biography:Gottfried Wilhelm Leibniz|Leibniz]]. Fermat was a trained lawyer making mathematics more of a hobby than a profession. Nevertheless, he made important contributions to analytical geometry, probability, number theory and calculus.<ref>{{Cite book|title=Essential Calculus: Early Transcendental Functions|last1=Larson|first1=Ron|last2=Hostetler|first2=Robert P.|last3=Edwards|first3=Bruce H.|publisher=Houghton Mifflin|year=2008|isbn=978-0-618-87918-2|location=Boston|pages=159}}</ref> Secrecy was common in European mathematical circles at the time. This naturally led to priority disputes with contemporaries such as [[Biography:René Descartes|Descartes]] and [[Biography:John Wallis|Wallis]].<ref name=ball>{{Cite book| last = Ball | first = Walter William Rouse | title = A short account of the history of mathematics | publisher = General Books LLC | year = 1888 | isbn = 978-1-4432-9487-4}}</ref>

[[Biography:Anders Hald|Anders Hald]] writes that, "The basis of Fermat's mathematics was the classical Greek treatises combined with Vieta's new algebraic methods."<ref>{{cite journal|last= Faltings|first= Gerd|issue= 7|journal= [[Organization:Notices of the American Mathematical Society|Notices of the American Mathematical Society]]|mr= 1335426|pages= 743–746|title= The proof of Fermat's last theorem by R. Taylor and A. Wiles|url= https://www.ams.org/notices/199507/faltings.pdf|volume= 42|year= 1995}}</ref>

===Work===
[[File:Diophantus-II-8-Fermat.jpg|thumb|right|upright| The 1670 edition of Diophantus's ''Arithmetica'' includes Fermat's commentary, referred to as his "Last Theorem" (''Observatio Domini Petri de Fermat''), posthumously published by his son]]
Fermat's pioneering work in [[Analytic geometry|analytic geometry]] (''Methodus ad disquirendam maximam et minimam et de tangentibus linearum curvarum'') was circulated in manuscript form in 1636 (based on results achieved in 1629),<ref>Daniel Garber, Michael Ayers (eds.), ''The Cambridge History of Seventeenth-century Philosophy, Volume 2'', Cambridge University Press, 2003, p. 754 n. 56.</ref> predating the publication of Descartes' famous ''[[La Géométrie|La géométrie]]'' (1637), which exploited the work.<ref>{{Cite encyclopedia|url=https://www.britannica.com/biography/Pierre-de-Fermat|title=Pierre de Fermat {{!}} Biography & Facts|encyclopedia=Encyclopedia Britannica|access-date=2017-11-14|language=en}}</ref> This manuscript was published posthumously in 1679 in ''Varia opera mathematica'', as ''Ad Locos Planos et Solidos Isagoge'' (''Introduction to Plane and Solid Loci'').<ref>[[Biography:Jan Gullberg|Gullberg, Jan]]. ''Mathematics from the birth of numbers'', W. W. Norton & Company; p. 548. {{isbn|0-393-04002-X}} {{isbn|978-0393040029}}</ref>

In ''Methodus ad disquirendam maximam et minimam'' and in ''De tangentibus linearum curvarum'', Fermat developed a method ([[Adequality|adequality]]) for determining maxima, minima, and [[Tangent|tangent]]s to various curves that was equivalent to [[Differential calculus|differential calculus]].<ref name=Pellegrino>{{cite web | last = Pellegrino | first = Dana | title=Pierre de Fermat | url=https://sites.math.rutgers.edu/~cherlin/History/Papers2000/pellegrino.html| access-date=2008-02-24}}</ref><ref>[[Biography:Florian Cajori|Florian Cajori]], "Who was the First Inventor of Calculus" The American Mathematical Monthly (1919) [https://books.google.com/books?id=5wxLAAAAYAAJ Vol.26]</ref> In these works, Fermat obtained a technique for finding the centers of gravity of various plane and solid figures, which led to his further work in [[Quadrature (mathematics)|quadrature]].

Fermat was the first person known to have evaluated the integral of general power functions. With his method, he was able to reduce this evaluation to the sum of [[Geometric series|geometric series]].<ref name=quadrature>{{cite journal|last1= Paradís|first1= Jaume|last2= Pla|first2= Josep|last3= Viader|first3= Pelegrí|issue= 1|journal= Revue d'Histoire des Mathématiques|mr= 2493381|zbl= 1162.01004|pages= 5–51|title= Fermat's method of quadrature|url= https://www.numdam.org/item/RHM_2008__14_1_5_0|volume= 14|year= 2008|url-status= dead|archive-url= https://web.archive.org/web/20190808150930/http://www.numdam.org/item/RHM_2008__14_1_5_0/|archive-date=2019-08-08}}</ref> The resulting formula was helpful to [[Biography:Isaac Newton|Newton]], and then [[Biography:Gottfried Wilhelm Leibniz|Leibniz]], when they independently developed the [[Fundamental theorem of calculus|fundamental theorem of calculus]].{{Citation needed|date=February 2008}}

In number theory, Fermat studied [[Pell's equation]], [[Perfect number|perfect number]]s, amicable numbers and what would later become Fermat numbers. It was while researching perfect numbers that he discovered [[Fermat's little theorem]]. He invented a factorization method—[[Fermat's factorization method]]—and popularized the proof by infinite descent, which he used to prove [[Fermat's right triangle theorem]] which includes as a corollary Fermat's Last Theorem for the case ''n'' = 4. Fermat developed the [[Fermat's theorem on sums of two squares|two-square theorem]], and the [[Fermat polygonal number theorem|polygonal number theorem]], which states that each number is a sum of three [[Triangular number|triangular number]]s, [[Lagrange's four-square theorem|four square numbers]], five pentagonal numbers, and so on.

Although Fermat claimed to have proven all his arithmetic theorems, few records of his proofs have survived. Many mathematicians, including [[Biography:Carl Friedrich Gauss|Gauss]], doubted several of his claims, especially given the difficulty of some of the problems and the limited mathematical methods available to Fermat. His famous [[Fermat's Last Theorem|Last Theorem]] was first discovered by his son in the margin in his father's copy of an edition of [[Biography:Diophantus|Diophantus]], and included the statement that the margin was too small to include the proof. It seems that he had not written to [[Biography:Marin Mersenne|Marin Mersenne]] about it. It was first proven in 1994, by [[Wiles's proof of Fermat's Last Theorem|Sir Andrew Wiles]], using techniques unavailable to Fermat.{{citation needed|date=April 2021}}

Through their correspondence in 1654, Fermat and [[Biography:Blaise Pascal|Blaise Pascal]] helped lay the foundation for the theory of probability. From this brief but productive collaboration on the [[Problem of points|problem of points]], they are now regarded as joint founders of [[Probability theory|probability theory]].<ref name=mactutor>{{cite web | last1 = O'Connor | first1 = J. J. | last2 = Robertson | first2 = E. F. | title=The MacTutor History of Mathematics archive: Pierre de Fermat | url=http://mathshistory.st-andrews.ac.uk/Biographies/Fermat.html| access-date=2008-02-24 }}</ref> Fermat is credited with carrying out the first-ever rigorous probability calculation. In it, he was asked by a professional gambler why if he bet on rolling at least one six in four throws of a die he won in the long term, whereas betting on throwing at least one double-six in 24 throws of two dice resulted in his losing. Fermat showed mathematically why this was the case.<ref>Eves, Howard. ''An Introduction to the History of Mathematics'', Saunders College Publishing, Fort Worth, Texas, 1990.</ref>

The first [[Physics:History of variational principles in physics|variational principle]] in [[Physics:Physics|physics]] was articulated by [[Biography:Euclid|Euclid]] in his ''Catoptrica''. It says that, for the path of light reflecting from a mirror, the [[Physics:Angle of incidence (optics)|angle of incidence]] equals the angle of reflection. [[Biography:Hero of Alexandria|Hero of Alexandria]] later showed that this path gave the shortest length and the least time.<ref>{{cite book|last=Kline|first=Morris|title=Mathematical Thought from Ancient to Modern Times|publisher=Oxford University Press|location=New York|year=1972|pages= 167–168 |isbn=978-0-19-501496-9}}</ref> Fermat refined and generalized this to "light travels between two given points along the path of shortest ''time''" now known as the ''principle of least time''.<ref name=variational>{{cite web |title=Fermat's principle for light rays | url=http://relativity.livingreviews.org/open?pubNo=lrr-2004-9&page=articlesu9.html | archive-url=https://web.archive.org/web/20160303235551/http://relativity.livingreviews.org/open?pubNo=lrr-2004-9&page=articlesu9.html | archive-date=March 3, 2016| access-date=2008-02-24}}</ref> For this, Fermat is recognized as a key figure in the historical development of the fundamental [[Physics:Principle of least action|principle of least action]] in physics. The terms [[Fermat's principle]] and ''Fermat functional'' were named in recognition of this role.<ref name=functional>{{cite journal|last=Červený |first=V. |date=July 2002 |title=Fermat's Variational Principle for Anisotropic Inhomogeneous Media |journal=Studia Geophysica et Geodaetica |volume=46 |issue=3 |doi=10.1023/A:1019599204028 |page=567 |s2cid=115984858 }}</ref>

===Death===
Pierre de Fermat died on January 12, 1665, at Castres, in the present-day department of Tarn.<ref name=barner>[https://web.archive.org/web/20080506074547/http://cat.inist.fr/?aModele=afficheN&cpsidt=14213014 Klaus Barner (2001): ''How old did Fermat become?''] Internationale Zeitschrift für Geschichte und Ethik der Naturwissenschaften, Technik und Medizin. {{issn|0036-6978}}. Vol 9, No 4, pp. 209-228.</ref> The oldest and most prestigious high school in Toulouse is named after him: the Lycée Pierre-de-Fermat. French sculptor Théophile Barrau made a marble statue named ''Hommage à Pierre Fermat'' as a tribute to Fermat, now at the Capitole de Toulouse.

<gallery widths="200px" heights="200px">
File:Fermat burial plaque.jpg|alt=Plaque at the place of burial of Pierre de Fermat |Place of burial of Pierre de Fermat in Place Jean Jaurés, Castres. Translation of the plaque: in this place was buried on January 13, 1665, Pierre de Fermat, councillor at the Chambre de l'Édit (a court established by the [[Religion:Edict of Nantes|Edict of Nantes]]) and mathematician of great renown, celebrated for his theorem,<br /> a<sup>n</sup> + b<sup>n</sup> ≠ c<sup>n</sup> for n>2
File:Beaumont-de-Lomagne - Monument à Fermat.jpg|Monument to Fermat in Beaumont-de-Lomagne in Tarn-et-Garonne, southern France
File:Capitole Toulouse - Salle Henri-Martin - Buste de Pierre de Fermat.jpg|Bust in the Salle Henri-Martin in the Capitole de Toulouse
File:Fermats will.jpg|Holographic will handwritten by Fermat on 4 March 1660, now kept at the Departmental Archives of Haute-Garonne, in Toulouse
</gallery>

==Assessment of his work==
Together with [[Biography:René Descartes|René Descartes]], Fermat was one of the two leading mathematicians of the first half of the 17th century. According to Peter L. Bernstein, in his 1996 book ''Against the Gods'', Fermat "was a mathematician of rare power. He was an independent inventor of [[Analytic geometry|analytic geometry]], he contributed to the early development of calculus, he did research on the weight of the earth, and he worked on light refraction and optics. In the course of what turned out to be an extended correspondence with [[Biography:Blaise Pascal|Blaise Pascal]], he made a significant contribution to the theory of probability. But Fermat's crowning achievement was in the theory of numbers."<ref name=Bernstein>{{cite book | last = Bernstein | first = Peter L. | title = Against the Gods: The Remarkable Story of Risk | publisher = John Wiley & Sons | year = 1996 | pages = [https://archive.org/details/againstgodsremar00pete_0/page/61 61–62] | isbn = 978-0-471-12104-6 | url-access = registration | url = https://archive.org/details/againstgodsremar00pete_0/page/61 }}</ref>

Regarding Fermat's work in analysis, [[Biography:Isaac Newton|Isaac Newton]] wrote that his own early ideas about calculus came directly from "Fermat's way of drawing tangents."<ref name=Simmons>{{cite book | last = Simmons | first = George F.|title= Calculus Gems: Brief Lives and Memorable Mathematics | url = https://archive.org/details/calculusgemsbrie0000simm | url-access = registration | publisher = Mathematical Association of America | year = 2007 | page = [https://archive.org/details/calculusgemsbrie0000simm/page/98 98] | isbn = 978-0-88385-561-4}}</ref>

Of Fermat's number theoretic work, the 20th-century mathematician [[Biography:André Weil|André Weil]] wrote that: "what we possess of his methods for dealing with [[Algebraic curve|curves]] of [[Elliptic curve|genus 1]] is remarkably coherent; it is still the foundation for the modern theory of such curves. It naturally falls into two parts; the first one ... may conveniently be termed a method of ascent, in contrast with the descent which is rightly regarded as Fermat's own."<ref>Weil 1984, p.104</ref> Regarding Fermat's use of ascent, Weil continued: "The novelty consisted in the vastly extended use which Fermat made of it, giving him at least a partial equivalent of what we would obtain by the systematic use of the [[Group theory|group theoretical]] properties of the [[Rational point|rational point]]s on a standard cubic."<ref>Weil 1984, p.105</ref> With his gift for number relations and his ability to find proofs for many of his theorems, Fermat essentially created the modern theory of numbers.

==See also==
* [[Diagonal form]]
* [[Euler's theorem]]
* List of things named after Pierre de Fermat

==Notes==
{{notelist}}

==References==
{{Reflist|30em}}

===Works cited===
*{{cite book | last = Weil | first = André  | title = Number Theory: An approach through history From Hammurapi to Legendre | publisher = Birkhäuser | year = 1984 |isbn =978-0-8176-3141-3}}

==Further reading==
*{{cite journal | author=Barner, Klaus | title=Pierre de Fermat (1601?–1665): His life besides mathematics | journal=Newsletter of the European Mathematical Society |date=December 2001 |pages=12–16}}
*{{cite book
 | author=Mahoney, Michael Sean
 | title=The mathematical career of Pierre de Fermat, 1601–1665
 | publisher=Princeton Univ. Press
 | year=1994
 | isbn=978-0-691-03666-3}}
*{{cite book|last=Singh|first=Simon|title=Fermat's Last Theorem|publisher=Fourth Estate Ltd|year=2002|isbn=978-1-84115-791-7|title-link=Fermat's Last Theorem (book)}}

==External links==
* [http://fermatslasttheorem.blogspot.com/2005/05/fermats-achievements.html Fermat's Achievements]
* [http://www.mathpages.com/home/kmath195/kmath195.htm Fermat's Fallibility] at MathPages
* [http://emlo-portal.bodleian.ox.ac.uk/collections/?catalogue=pierre-de-fermat The Correspondence of Pierre de Fermat] in [http://emlo.bodleian.ox.ac.uk/ EMLO]
* [https://web.archive.org/web/20080617221136/http://ns33717.ovh.net/spokus/default/EN/all/tpe_felix/ History of Fermat's Last Theorem (French)]
* The [http://www.maths.tcd.ie/pub/HistMath/People/Fermat/RouseBall/RB_Fermat.html Life and times of Pierre de Fermat (1601–1665)] from W. W. Rouse Ball's History of Mathematics
* {{MacTutor Biography|id=Fermat}}

{{Infinitesimals}}

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[[Category:Number theorists]]

{{Sourceattribution|Pierre de Fermat}}