Elias Costa

Member for 12 years
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Brasília, DF, Brasil

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real-analysis

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44

How can I prove that $xy\leq x^2+y^2$?

Apr 10, 2013

39

How does a non-mathematician go about publishing a proof in a way that ensures it to be up to the mathematical community's standards?

Jan 10, 2013

25

Why the $\nabla f(x)$ in the direction orthogonal to $f(x)$?

May 25, 2013

21

Can't argue with success? Looking for "bad math" that "gets away with it"

Dec 18, 2012

15

Funny identities

Jan 13, 2013

Questions

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114

On the Constant Rank Theorem and the Frobenius Theorem for differential equations.

Jun 22, 2013

63

How to prove that a compact set in a Hausdorff topological space is closed?

Nov 18, 2011

31

A simple way to obtain $\prod_{p\in\mathbb{P}}\frac{1}{1-p^{-s}}=\sum_{n=1}^{\infty}\frac{1}{n^s}$.

Jun 24, 2013

25

Prove that $2018^{2019}> 2019^{2018}$ without induction, without Newton's binomial formula and without Calculus.

Feb 25, 2019

20

The problem of the most visited point.

Dec 24, 2013

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real-analysis

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calculus

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integration

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soft-question

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linear-algebra

63

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+10

How to prove that a compact set in a Hausdorff topological space is closed?

+10

On Ph.D. Qualifying Exams

+10

Equivalence between Brouwer fixed-point theorem and Borsuk-Ulam theorem. Is there a simple proof of equivalence between them?

+10

On the Constant Rank Theorem and the Frobenius Theorem for differential equations.

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