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Mathematics : Recent Questions and Answers (Page 91)

Find answers to your questions about Mathematics or help others by answering their Mathematics questions.

Is the minimum of this functional $C^{infty}$?

The problem: Let us define$$mathscr{F}(u)=int_0^1(u'(x))^4-e^xsin (u(x)), mathrm{d}x$$for $u in W^{1,1}([0,1])$ such that $u(0)=A$ and $u(1)=B$.It don't matters what $A$ or...

Asked on 11/09/2021

0 answer

Formula for Repeated Derivatives

Does there exist a formula akin to Cauchy's Repeated Integration formula, but for derivatives? Cauchy's formula doesn't seem ideal for finding, say, the 100th derivative of a function as factorials...

Asked on 11/09/2021

1 answer

Need help understanding the last step of the proof of this lemma involving probabilities

Lemma : Suppose that the events $A_{1}, ldots, A_{n}$ satisfy $operatorname{Var}left(sum_{i=1}^{n} I_{A_{i}}right) leq c sum_{i=1}^{n} Pleft{A_{i}right} .$ Then :$$ left(1-Pleft(bigcup_{k=1}^{n} A_{k}right)right)^{2} sum_{i=1}^{n} Pleft{A_{i}right} leq c Pleft(bigcup_{k=1}^{n}...

Asked on 11/09/2021

2 answer

Proof: For $n in mathbb{Z_+}$, the set of all functions $f: {1,...,n} to mathbb{Z_+}$ is countable

(citation: Munkres Topology 7.5 b) Backgound (from Munkres Topology Chapter 7): Theorem 7.1: $B$ is a nonempty countable set $LeftarrowRightarrow$ there is an injective function $g:...

Asked on 11/09/2021

1 answer

Compute the following product limit

From another problem, I got stuck trying to solve this limit: $$lim_{kto +infty}prod_{v=k+1}^{2k}left(1-frac1{va}right)$$where $a>1$ is a positive integer. I tried to take $log$ on both sides...

Asked on 11/09/2021

3 answer

Show that $(sum a_{n}^{3} sin n)$ converges given $sum{a_n}$ converges

Given that $sum a_{n}$ converges $left(a_{n}>0right) ;$ Then $(sum a_{n}^{3} sin n)$ isMy approach: Since, $sum a_{n}$ converges, we have $lim _{n rightarrow infty}...

Asked on 11/09/2021 by user791682

2 answer

Remarkable logarithmic integral $int_0^1 frac{log^2 (1-x) log^2 x log^3(1+x)}{x}dx$

We have the following result ($text{Li}_{n}$ being the polylogarithm): $$tag{*}small{ int_0^1 log^2 (1-x) log^2 x log^3(1+x) frac{dx}{x} = -168 text{Li}_5(frac{1}{2}) zeta (3)+96 text{Li}_4(frac{1}{2}){}^2-frac{19}{15} pi ^4 text{Li}_4(frac{1}{2})+\ 12 pi...

Asked on 11/09/2021

2 answer

Prove that $512^3 + 675^3 + 720^3$ is a composite number

We have to prove that the number $$N=512^3 + 675^3 + 720^3$$ is composite.I tried to use the identity $(a^3+b^3+c^3)=(a+b+c)(a^2+b^2+c^2-ab-bc-ca)+3abc$ hoping to take...

Asked on 11/09/2021

1 answer

How to prove that $lim_{kto+infty}frac{sin(kx)}{pi x}=delta(x)$?

It is well-known that:$$lim_{kto+infty}frac{sin(kx)}{pi x}=delta(x).$$This can also be written as$$ 2pidelta(x)=int^{+infty}_{-infty}e^{ikx},mathrm dk.$$However, I don't know how to prove this without using Fourier Transform. I...

Asked on 11/09/2021 by lrh2000

4 answer

Induction. Circular track and fuel stations

The sides of a circular track contain a sequence of cans of gasoline. The total amount in the cans is sufficient to enable a certain car to make one complete...

Asked on 11/09/2021

2 answer

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