mathematics

Thomas Fantet de Lagny

Thomas Fantet de Lagny is a mathematics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Thomas Fantet de Lagny rather than just read about it. In short: Thomas Fantet de Lagny (7 November 1660 – 11 April 1734) was a French mathematician, well known for his contributions to computational mathematics, and for calculating π to 112 correct decimal places. Biography Thomas Fantet de Lagny was son of Pierre Fantet, a royal official in Grenoble, and Jeanne d'Azy, the daughter of a physician from Montpellier.

Key takeaways

Thomas Fantet de Lagny belongs to mathematics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Thomas Fantet de Lagny to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thomas Fantet de Lagny from memory before moving on to harder problems.

Reference excerpt

Biography Thomas Fantet de Lagny was son of Pierre Fantet, a royal official in Grenoble, and Jeanne d'Azy, the daughter of a physician from Montpellier. He entered a Jesuit College in Lyon, where he became passionate about mathematics, as he studied some mathematical texts such as Euclid by Georges Fournier and an algebra text by Jacques Pelletier du Mans. Then he studied three years in the Faculty of Law in Toulouse. In 1686, he went to Paris and became a mathematics tutor to the Noailles family. He collaborated with de l'Hospital under the name of de Lagny, and at that time he started publishing his first mathematical papers. He came back to Lyon when, on 11 December 1695, he was named an associate of the Académie Royale des Sciences. Then, in 1697, he became professor of hydrography at Rochefort for 16 years. De Lagny returned to Paris in 1714, and became a librarian at the Bibliothèque du roi, and a deputy director of the Banque Générale between 1716 and 1718. On 7 July 1719, he was awarded a pension by the Académie Royale des Sciences, finally earning his living from science. In 1723, he became a pensionnaire at the academy, replacing Pierre Varignon who died in 1722, but had to retire in 1733. De Lagny died on 11 April 1734. While he was dying, someone asked him: "What is the square of 12?" and he answered immediately: "144."

Computing π In 1719, de Lagny calculated π to 127 decimal places, using Gregory's series for arctangent, but only 112 decimals were correct. This remained the record until 1789, when Jurij Vega calculated 126 correct digits of π.

Bibliography Méthode nouvelle infiniment générale et infiniment abrégée pour l’extraction des racines quarrées, cubiques... (Paris, 1691) Méthodes nouvelles et abrégées pour l’extraction et l’approximation des racines (Paris, 1692) Nouveaux élémens d’arithmétique et d’algébre ou introduction aux mathématiques (Paris, 1697) Trignonmétrie française ou reformée (Rochefort, 1703) De la cubature de la sphére où l’on démontr une infinité de portions de sphére égales à des pyramides rectilignes (La Rochelle, 1705) Analyse générale ou Méthodes nouvelles pour résoudre les probémes de tous les genres et de tous degrés à l’infini, M. Richer, ed. (Paris, 1733)

References O'Connor, John J.; Robertson, Edmund F., "Thomas Fantet de Lagny", MacTutor History of Mathematics Archive, University of St Andrews Lagny, Thomas Fantet de, Encyclopedia.com

Illustrations

Worked examples

Example 1 — a first encounter with Thomas Fantet de Lagny

Start with the simplest possible case. Write down what Thomas Fantet de Lagny claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In mathematics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Thomas Fantet de Lagny before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Thomas Fantet de Lagny ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Thomas Fantet de Lagny

In research: Thomas Fantet de Lagny appears in mathematics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Thomas Fantet de Lagny in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Thomas Fantet de Lagny is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1660 births, 1734 deaths, French mathematicians, so understanding it makes those chapters shorter.
In everyday life: Look for Thomas Fantet de Lagny outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Thomas Fantet de Lagny in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thomas Fantet de Lagny means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Thomas Fantet de Lagny out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thomas Fantet de Lagny in simple terms?

Thomas Fantet de Lagny (7 November 1660 – 11 April 1734) was a French mathematician, well known for his contributions to computational mathematics, and for calculating π to 112 correct decimal places. Biography Thomas Fantet de Lagny was son of Pierre Fantet, a royal official in Grenoble, and Jeann…

Why does Thomas Fantet de Lagny matter?

Because it connects several mathematics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Thomas Fantet de Lagny?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Thomas Fantet de Lagny.