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History and philosophy of mathematics, biographies of mathematicians, mathematics education, recreational mathematics, communication of mathematics.

29 votes
Accepted

How did Bernoulli prove L'Hôpital's rule?

L'Hôpital's rule was first published in Analyse des Infiniment Petits. According to The Historical Development of The Calculus by Edwards (p. 269), L'Hospital's argument, which is stated verbally w …
Andrey Rekalo's user avatar
28 votes

Abstract thought vs calculation

Hilbert's finiteness theorem, which arguably "killed classical invariant theory" and resulted in the creation of abstract algebra. Hilbert's first work on invariant functions led him to the demonstra …
26 votes

What are some correct results discovered with incorrect (or no) proofs?

According to Weierstrass, Riemann knew about the existence of continuous nowhere differentiable functions. (Weierstrass' celebrated example was published in 1872, some 6 years after Riemann's death.) …
26 votes
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What was Weierstrass's counterexample to the Dirichlet Principle?

Weierstrass simply observed that not every problem in the calculus of variations would have a solution. He considered the example $$D[y]=\int_{-1}^{1}x^2\left(\frac{d y}{dx}\right)^2dx\to \min,$$ wher …
Andrey Rekalo's user avatar
24 votes

Why are differential forms called closed and exact?

According to Hans Samelson's historical note "Differential Forms, the Early Days", both notions were introduced in Les Méthodes nouvelles de la Mécanique Céleste by Poincaré (vol. 3, Gauthier-Villar …
Andrey Rekalo's user avatar
24 votes

What are some correct results discovered with incorrect (or no) proofs?

Riemann's flawed proof of the Riemann mapping theorem which crucially relied on Dirichlet's principle. The theorem was stated by Bernhard Riemann in 1851 in his PhD thesis. Lars Ahlfors wrote once, c …
20 votes

Source and context of $\frac{22}{7} - \pi = \int_0^1 (x-x^2)^4 dx/(1+x^2)$?

Jonathan M. Borwein, David H. Bailey and Roland Girgensohn discuss this and related formulae for $\pi$ in their book "Experimentation in Mathematics" (see Section 1.1, p. 3). They claim that The i …
Andrey Rekalo's user avatar
17 votes

A question regarding a claim of V. I. Arnold

The limit $$ \lim_{x\to 0}\frac { f(x) - g(x) } { f^{-1}(x) - g^{-1}(x)} = -\left(f'(0)\right)^6 $$ appears in the Problems section of Mathematics Magazine, where it is calculated under the assumptio …
Andrey Rekalo's user avatar
14 votes

Countable connected Hausdorff space

Urysohn's example of a countable connected Hausdorff space with a countable base was published in his last paper «Über die Mächtigkeit der zusammenhängenden Mengen», Math Annalen 94 (1925), 262—295. …
Andrey Rekalo's user avatar
14 votes
Accepted

The Ramanujan Problems

There is a survey article by Berndt, Choi, and Kang devoted to the set of 58 Ramanujan's problems. They indicate that the questions had originally appeared in the problems section of the Journal and a …
Andrey Rekalo's user avatar
12 votes
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Where does the Chebyshev polynomial notation come from?

Great Soviet mathematician N.I. Akhiezer mentions in his survey article "Чебышевское направление в теории функций" ("Function Theory According to Chebyshev") that the notation $$T_n(x)=\frac{1}{2^{n- …
Andrey Rekalo's user avatar
10 votes

What is the naming reason of poles in complex analysis?

According to these pages, the earliest known appearance of the term pole might be in "Théorie des fonctions elliptiques" (1875, p. 15) by Briot and Bouquet: Lorsqu'une fonction $u$ est holomorph …
10 votes

What are Central Limit Theorems and why are they called so?

From the introduction to History of the Central Limit Theorem: From Laplace to Donsker by Hans Fischer: The term “central limit theorem” most likely traces back to Georg Pólya. As he recapitulat …
Andrey Rekalo's user avatar
9 votes
Accepted

English or French translation of Gauss' "Summatio Quarumdam Serierum Singularium"

"The determination of Gauss sums" by Berndt and Evans (Bull. Amer. Math. Soc., Vol. 5, Number 2 (1981), 107-129.) contains an exposition of the original proof due to Gauss. It also includes a short hi …
Andrey Rekalo's user avatar
8 votes
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Fibonacci = Leonardo Pisano?

From The Fabulous Fibonacci Numbers by A.S. Posamentier and I. Lehmann (Prometheus Books, New York (2007), pp. 17-18): Leonardo Pisano - or Leonardo of Pisa, Fibonacci - his name as recorded in hi …
Andrey Rekalo's user avatar

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