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Forum: Real Analysis   Topic: A Riemann type sum

 Post subject: A Riemann type sum Posted: Sat May 18, 2019 9:09 pm

Replies: 0
Views: 72

 Justify the fact that$$\frac{1}{m} \sum_{j=1}^{m} \left(\frac{2j-1}{m}-1\right) \log \left(\frac{j}{m}\right) \xrightarrow[m \rightarrow +\infty]{} \int_{0}^{1} (2x-1)\log x \, \mathrm{d}x =\frac{1}{2}$$ Forum: Calculus   Topic: Analytic series

 Post subject: Analytic series Posted: Thu Mar 28, 2019 12:56 pm

Replies: 0
Views: 70

 Evaluate in a closed form the series:$$\mathcal{S} = \sum_{n=-\infty}^{\infty} \frac{16}{\left ( 4n^2+n+5 \right )^2}$$ Forum: General Mathematics   Topic: A sum!

 Post subject: Re: A sum! Posted: Thu Feb 07, 2019 4:57 pm

Replies: 4
Views: 771

 First of all note that $10! = 2^8 \cdot 3^4 \cdot 5^2 \cdot 7$ hence ⋅ $10!$ is not a perfect square, ⋅ $10!$ has $(8+1)(4+1)(2+1)(1+1) = 270$ divisors. If $d \mid 10!$ , then there exists $p$ such that $dp =10!$ meaning that $p$ is also a divisor of $10!$. We also note that if o... Forum: General Topology   Topic: A log metric

 Post subject: A log metric Posted: Tue Jan 08, 2019 11:05 am

Replies: 0
Views: 117

 Endow $(0, +\infty)$ with the following metric$$d(x, y) = \left | \log \frac{x}{y} \right |$$(i) Verify that $d$ is indeed a metric.(ii) Is the sequence $a_n =\frac{1}{n}$ convergent under this metric? Give a brief explanation.(iii) Examine if $(0, +\infty)$ is bounded under this metric. Post subject: Re: Find the number of homomorphism Posted: Thu Dec 06, 2018 7:43 pm

Replies: 1
Views: 172

 Hi Ram_1729. Could you explain what $Q_8$ and $K_4$ stand for? Posted: Thu Dec 06, 2018 7:43 pm

Replies: 2
Views: 434

 Thank you Ram_1729. Exactly! It was an exam's question! Forum: General Mathematics   Topic: An inequality

 Post subject: An inequality Posted: Thu Nov 22, 2018 9:26 pm

Replies: 0
Views: 119

 Let $x_1, x_2, \dots, x_n$ be $n \geq 2$ positive numbers other than $1$ such that $x_1^2+x_2^2+\cdots +x_n^2=n^3$. Prove that:$$\frac{\log_{x_1}^4 x_2}{x_1+x_2}+ \frac{\log_{x_2}^4 x_3}{x_2+x_3}+ \cdots + \frac{\log_{x_n}^4 x_1}{x_n+x_1} \geq \frac{1}{2}$$ Forum: Algebraic Structures   Topic: Symetry group of Tetrahedron

 Post subject: Re: Symetry group of Tetrahedron Posted: Tue Nov 06, 2018 4:48 pm

Replies: 2
Views: 289

 ⋅ The tetrahedron is a regular solid with $4$ vertices and $4$ triangular faces. The symmetry group is the alternating group $\mathcal{A}_4$. ⋅ The symmetry group of a cube is isomorphic to $\mathcal{S}_4$ , the permutation group on 4 elements. If we number the vertices of the c... Forum: Linear Algebra   Topic: Computation of determinant

 Post subject: Computation of determinant Posted: Tue Oct 16, 2018 10:26 am

Replies: 0
Views: 175

 Let $A, B \in \mathcal{M}_{2 \times 2}$ be matrices with integer entries such that $AB = BA$ , $\det \left( A + B \right) =2$ and $\det \left( A^3 + B^3 \right) = 2^3$. Evaluate the determinant$$\mathcal{D} = \det \left( A^2 + B^2 \right)$$ Forum: Calculus   Topic: Series with general harmonic number

 Post subject: Series with general harmonic number Posted: Sun Aug 12, 2018 8:27 pm

Replies: 0
Views: 215

 Let $\mathcal{H}_n$ denote the $n$ - th harmonic number. It holds that $$\sum\limits_{n=1}^{\infty}\mathcal{H}_{pn}x^n = -\frac{1}{p}\sum\limits_{k=0}^{p-1} \frac{\ln \varphi_k}{\varphi_k}$$ where $p \in \mathbb{N}$ and \$\displaystyle \varphi_k = \varphi_k(x) = 1 - \sqrt[p]{x}\exp\left(\frac{-2\pi i... Sort by:
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