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jlacosta   0
Apr 2, 2025
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0 replies
jlacosta
Apr 2, 2025
0 replies
2025 OMOUS Problem 1
enter16180   1
N 2 hours ago by KAME06
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Aman and Berdi, two biologists, they invented a new type of bacteria such that they can control the division of bacteria into several parts. They are also participants of $OMOUS-2025$ with the aim to train for the first problem of $OMOUS-2025$. They play the following game.
Initially, they take $1$ bacteria and choose a natural number $n$. On each move, the player chooses any $k$ number from $1$ to $n$. Then the player divides each bacterium into $k$ pants. Once chosen, the number $k$ cannot be chosen twice. If after any player's move the number of bacteria population is divisible by $n$ then that player loses. Determine who has the winning strategy depending on the given number $n$ if it's known that Amman starts first.
1 reply
enter16180
Today at 11:44 AM
KAME06
2 hours ago
Interesting Limit
Riptide1901   0
3 hours ago
Find $\displaystyle\lim_{x\to\infty}\left|f(x)-\Gamma^{-1}(x)\right|$ where $\Gamma^{-1}(x)$ is the inverse gamma function, and $f^{-1}$ is the inverse of $f(x)=x^x.$
0 replies
Riptide1901
3 hours ago
0 replies
Sequence of functions
Squeeze   1
N 4 hours ago by Squeeze
Q) let $f_n:[-1,1)\to\mathbb{R}$ and $f_n(x)=x^{n}$ then is this uniformly convergence on $(0,1)$ comment on uniformly convergence on $[0,1]$ where in general it is should be uniformly convergence.

My I am trying with some contradicton method like chose $\epsilon=1$ and trying to solve$|f_n(a)-f(a)|<\epsilon=1$
Next take a in (0,1) and chose a= 2^1/N but not solution
How to solve like this way help.
1 reply
Squeeze
Today at 3:56 AM
Squeeze
4 hours ago
Integrate lnx/sqrt{1-x^2}
EthanWYX2009   1
N 5 hours ago by GreenKeeper
Determine the value of
\[I=\int\limits_{0}^{1}\frac{\ln x}{\sqrt{1-x^2}}\mathrm dx.\]
1 reply
EthanWYX2009
Today at 2:38 PM
GreenKeeper
5 hours ago
OMOUS-2025 (Team Competition) P6
enter16180   1
N Today at 2:38 PM by MS_asdfgzxcvb
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Let $f:[-1,1] \rightarrow \mathbb{R}$ be a continuous function such that $\int_{-1}^{1} x^{2} f(x) d x=0$. Prove that

$$
8 \int_{-1}^{1} f^{2}(x) d x \geq\left(\int_{-1}^{1} 3 f(x) d x\right)^{2}
$$
1 reply
enter16180
Today at 12:03 PM
MS_asdfgzxcvb
Today at 2:38 PM
2025 OMOUS Problem 2
enter16180   1
N Today at 1:32 PM by Figaro
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Compute

$$
\prod_{n=1}^{\infty} \frac{(2 n)^{4}-1}{(2 n+1)^{4}-1} \frac{n^{2}}{(n+1)^{2}} .
$$
1 reply
enter16180
Today at 11:44 AM
Figaro
Today at 1:32 PM
Integrate exp(x-10cosh(2x))
EthanWYX2009   1
N Today at 1:16 PM by GreenKeeper
Source: 2024 May taca-14
Determine the value of
\[I=\int\limits_{-\infty}^{\infty}e^{x-10\cosh (2x)}\mathrm dx.\]
1 reply
EthanWYX2009
Today at 5:20 AM
GreenKeeper
Today at 1:16 PM
Linear Space Decomposition
Suan_16   0
Today at 12:46 PM
Let $A$ be a linear transformation on linear space $V$ satisfying:$$A^l=0$$but $$A^{l-1} \neq 0$$, and $V_0$ is the eigensubspace of eigenvalue $0$. Prove that $V$ can be decomposed to $dim V_0$ $A$-cyclic subspace's direct sum.

Click to reveal hidden text
0 replies
Suan_16
Today at 12:46 PM
0 replies
The Relationship Between Function and Ordering Relation
mathservant   0
Today at 12:35 PM
I think, the necessary and sufficient condition for a function to induce an ordering relation (specifically a partial or total order) on its domain is that it must be compatible with the ordering defined on the codomain (i.e., it must be order-preserving).

How can we express this necessary and sufficient condition more clearly? Thank you.
0 replies
mathservant
Today at 12:35 PM
0 replies
Jordan form and canonical base of a matrix
And1viper   1
N Today at 12:30 PM by Suan_16
Find the Jordan form and a canonical basis of the following matrix $A$ over the field $Z_5$:
$$A = \begin{bmatrix}
    2 & 1 & 2 & 0 & 0 \\
    0 & 4 & 0 & 3 & 4 \\
    0 & 0 & 2 & 1 & 2 \\
    0 & 0 & 0 & 4 & 1 \\
    0 & 0 & 0 & 0 & 2
  \end{bmatrix}
$$
1 reply
And1viper
Feb 26, 2023
Suan_16
Today at 12:30 PM
OMOUS-2025 (Team Competition) P10
enter16180   0
Today at 12:11 PM
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Let $f: \mathbb{N} \rightarrow \mathbb{N}$ and $g: \mathbb{N} \rightarrow\{A, G\}$ functions are given with following properties:
(a) $f$ is strict increasing and for each $n \in \mathbb{N}$ there holds $f(n)=\frac{f(n-1)+f(n+1)}{2}$ or $f(n)=\sqrt{f(n-1) \cdot f(n+1)}$.
(b) $g(n)=A$ if $f(n)=\frac{f(n-1)+f(n+1)}{2}$ holds and $g(n)=G$ if $f(n)=\sqrt{f(n-1) \cdot f(n+1)}$ holds.

Prove that there exist $n_{0} \in \mathbb{N}$ and $d \in \mathbb{N}$ such that for all $n \geq n_{0}$ we have $g(n+d)=g(n)$
0 replies
enter16180
Today at 12:11 PM
0 replies
OMOUS-2025 (Team Competition) P9
enter16180   0
Today at 12:09 PM
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Let $\left\{a_{i}\right\}_{i=1}^{3}$ and $\left\{b_{i}\right\}_{i=1}^{3}$ be nonnegative numbers and $C:=\left\{c_{i j}\right\}_{i, j=1}^{3}$ be a nonnegative symmetric matrix such that $c_{11}=c_{22}=c_{33}=0$. Given $d>0$, consider the quadratic form

$$
Q(x)=\sum_{i=1}^{3} a_{i} x_{i}^{2}+\sum_{i=1}^{3} a_{i}\left(d-x_{i}\right)^{2}+\sum_{i, j=1}^{3} c_{i j}\left(x_{i}-x_{j}\right)^{2}, \quad x=\left(x_{1}, x_{2}, x_{3}\right) \in R^{3} .
$$Assume that

$$
\sum_{i=1}^{3} a_{i}>0, \quad \sum_{i=1}^{3} b_{i}>0,
$$
and for any $i, j$ there exists $m_{i j}>0$ such that $(i, j)$-the entry of the $m_{i j}$-th power $C^{m_{i j}}$ of $C$ is positive. Show that $Q$ has a unique minimum and the minimum lies in the open cube $(0, d)^{3}$ in $R^{3}$.
0 replies
enter16180
Today at 12:09 PM
0 replies
OMOUS-2025 (Team Competition) P8
enter16180   0
Today at 12:07 PM
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Find all functions $f:\left(\frac{\pi}{2025}, \frac{2024}{20225} \pi\right) \rightarrow \mathbb{R}$ such that for all $x, y \in\left(\frac{\pi}{2025}, \frac{2024}{20225} \pi\right)$, we have

$$
\sin y f(x)-\sin x f(y) \leq \sqrt[2025]{(x-y)^{20226}}
$$
0 replies
enter16180
Today at 12:07 PM
0 replies
OMOUS-2025 (Team Competition) P7
enter16180   0
Today at 12:04 PM
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Let $R$ be a ring not assumed to have an identity, with the following properties:
(i) There is an element of $R$ that is not nilpotent.
(ii) If $x_{1}, \ldots, x_{2024}$ are nonzero elements of $R$, then $\sum_{j=1}^{2024} x_{j}^{2025}=0$.

Show that $R$ is a division ring, that is, the nonzero elements of R form a group under multiplication.
0 replies
enter16180
Today at 12:04 PM
0 replies
polynomial with real coefficients
Peter   9
N Apr 15, 2025 by Rohit-2006
Source: IMC 1998 day 1 problem 5
Let $P$ be a polynomial of degree $n$ with only real zeros and real coefficients.
Prove that for every real $x$ we have $(n-1)(P'(x))^2\ge nP(x)P''(x)$. When does equality occur?
9 replies
Peter
Nov 1, 2005
Rohit-2006
Apr 15, 2025
polynomial with real coefficients
G H J
Source: IMC 1998 day 1 problem 5
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Peter
3615 posts
#1 • 2 Y
Y by Adventure10, Mango247
Let $P$ be a polynomial of degree $n$ with only real zeros and real coefficients.
Prove that for every real $x$ we have $(n-1)(P'(x))^2\ge nP(x)P''(x)$. When does equality occur?
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Diogene
808 posts
#2 • 3 Y
Y by dinamometre1123, Adventure10, Mango247
I will proceed by induction. For $n=1$ that's manifestly true. Let $P$ be polynomial of degree $n+1$ , so
$P(x)=u(x)Q(x)$ where $u(x)$ is a monic real polynomial of degree $1$ and $Q(x)$ is a polynomial of degree $n$ with only real roots and real coefficients.
$P(x)=u(x)Q(x) \Longrightarrow P'= Q+uQ'\Longrightarrow P'' = 2Q' + uQ''$ , where $(n-1)(Q')^2\geq nQQ''$ , so :

$n(P')^2-(n+1)PP'' = nQ^2-2uQQ'+nu^2(Q')^2-(n+1)u^2QQ''\geq$$nQ^2-2uQQ' + \frac{u^2(Q')^2}n = (Q\sqrt n - \frac{uQ'}{\sqrt n})^2 \geq 0$... (q.e.d)
:cool:
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Diogene
808 posts
#3 • 3 Y
Y by Adventure10, Mango247, Rohit-2006
Sorry, I forgot the equality case ! Remember : $u(x)$ is a monic real polynomial , $u(x) = x-a$
$n(P')^2-(n+1)PP'' = 0 \Longrightarrow Q\sqrt n - \frac{uQ'}{\sqrt n} = 0 \Longrightarrow \frac{Q'}{Q} = \frac nu$$\Longrightarrow Q(x)= cu^n_{(x)}\Longrightarrow P(x)=c u^{n+1}_{(x)}$
Also, It's easy to verify that the equality holds for $P(x)=c u^{n+1}_{(x)}$
:cool:
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bandrak
17 posts
#4 • 2 Y
Y by Davrbek, Adventure10
without induction, by the condition we have that
\[ P = b\prod^n_{i=1} (x-a_i)\]
Suppose $ x$ is not a root of $ P$ and Let $ c_i = \frac{1}{x-a_i}$, then
\[ P' = P (c_1 + c_2 + \ldots + c_n), P'' = P (\sum_{i \neq j} 2c_i c_j)\]
The problem thus becomes
\[ (n-1)(c_1 + c_2 + \ldots + c_n)^2 \ge 2n (\sum_{i \neq j}c_i c_j)\]
factoring gives
\[ \sum_{i \neq j} (c_i - c_j)^2 \ge 0\]
Which is trivially true. Also the equality holds iff all the $ c_i$ are equal, which means all the $ a_i$ are equal and $ P=b(x-a)^n$
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chakrabortyahan
379 posts
#5
Y by
Another solution
Let $\alpha_1,\alpha_2,...\alpha_n$ be the zeroes (non-necessarily distinct) of $P$. The given inequality holds trivially for $\alpha_i's$. So we assume that $x\neq \alpha_i$ in the latter part of the solution.
Now note that $P'(x) = P(x) [\sum_{i=1}^n\frac{1}{x-\alpha_i}]$
Now by C-S inequality ,
$$n\cdot\sum\limits_{i=1}^n\frac{1}{(x-\alpha_i)^2}\ge \left[ \sum\limits_{i=1}^n\frac{1}{|x-\alpha_i|}\right]^2\ge \left[\sum\limits_{i=1}^n\frac{1}{x-\alpha_i}\right]^2...(i)$$
Now note that $(i)$ can be re-written as $-n\left[\frac{P'(x)}{P(x)}\right]'\ge \left[\frac{P'(x)}{P(x)}\right]^2\iff 0\ge \frac{n(P''(x)P(x)-P'(x)^2)}{P(x)^2}+\frac{P'(x)^2}{P(x)^2}$
Hence proved as $P(x)^2> 0 $ for all $x\neq \alpha_i$
And the equality holds iff all $\alpha_i$ s are equal (equality case of Cauchy -Schewarz)
$\blacksquare\smiley$
This post has been edited 1 time. Last edited by chakrabortyahan, May 5, 2024, 6:22 PM
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Moubinool
5566 posts
#6
Y by
This problem was used for oral examination ENS PSLR in 2023
problem 23 oral PSLR
https://www.rms-math.com/exos-etoiles-2023-site.pdf
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mqoi_KOLA
85 posts
#7
Y by
chakrabortyahan wrote:
Another solution
Let $\alpha_1,\alpha_2,...\alpha_n$ be the zeroes (non-necessarily distinct) of $P$. The given inequality holds trivially for $\alpha_i's$. So we assume that $x\neq \alpha_i$ in the latter part of the solution.
Now note that $P'(x) = P(x) [\sum_{i=1}^n\frac{1}{x-\alpha_i}]$
Now by C-S inequality ,
$$n\cdot\sum\limits_{i=1}^n\frac{1}{(x-\alpha_i)^2}\ge \left[ \sum\limits_{i=1}^n\frac{1}{|x-\alpha_i|}\right]^2\ge \left[\sum\limits_{i=1}^n\frac{1}{x-\alpha_i}\right]^2...(i)$$
Now note that $(i)$ can be re-written as $-n\left[\frac{P'(x)}{P(x)}\right]'\ge \left[\frac{P'(x)}{P(x)}\right]^2\iff 0\ge \frac{n(P''(x)P(x)-P'(x)^2)}{P(x)^2}+\frac{P'(x)^2}{P(x)^2}$
Hence proved as $P(x)^2> 0 $ for all $x\neq \alpha_i$
And the equality holds iff all $\alpha_i$ s are equal (equality case of Cauchy -Schewarz)
$\blacksquare\smiley$


$$n\cdot\sum\limits_{i=1}^n\frac{1}{(x-\alpha_i)^2}\ge \left[ \sum\limits_{i=1}^n\frac{1}{|x-\alpha_i|}\right]^2\ge \left[\sum\limits_{i=1}^n\frac{1}{x-\alpha_i}\right]^2...(i)$$
why did you have modulus here in the thing between? CS inequality is true for all reals right
This post has been edited 1 time. Last edited by mqoi_KOLA, Mar 24, 2025, 11:39 AM
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quasar_lord
223 posts
#8
Y by
@above $\alpha_i$ can be complex ig?
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mqoi_KOLA
85 posts
#9
Y by
quasar_lord wrote:
@above $\alpha_i$ can be complex ig?

its given in q P has all real zeroes
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Rohit-2006
213 posts
#10
Y by
chakrabortyahan wrote:
Another solution
Let $\alpha_1,\alpha_2,...\alpha_n$ be the zeroes (non-necessarily distinct) of $P$. The given inequality holds trivially for $\alpha_i's$. So we assume that $x\neq \alpha_i$ in the latter part of the solution.
Now note that $P'(x) = P(x) [\sum_{i=1}^n\frac{1}{x-\alpha_i}]$
Now by C-S inequality ,
$$n\cdot\sum\limits_{i=1}^n\frac{1}{(x-\alpha_i)^2}\ge \left[ \sum\limits_{i=1}^n\frac{1}{|x-\alpha_i|}\right]^2\ge \left[\sum\limits_{i=1}^n\frac{1}{x-\alpha_i}\right]^2...(i)$$
Now note that $(i)$ can be re-written as $-n\left[\frac{P'(x)}{P(x)}\right]'\ge \left[\frac{P'(x)}{P(x)}\right]^2\iff 0\ge \frac{n(P''(x)P(x)-P'(x)^2)}{P(x)^2}+\frac{P'(x)^2}{P(x)^2}$
Hence proved as $P(x)^2> 0 $ for all $x\neq \alpha_i$
And the equality holds iff all $\alpha_i$ s are equal (equality case of Cauchy -Schewarz)
$\blacksquare\smiley$

Dada nvm....I don't think it's a complete solution because in the question said that for all $x$ but you are excluding the roots.....this is the first problem
The second problem is you are only told that degree is $n$ so I can consider that $n=0$ but in that case if it's a constant polynomial then it has infinite roots...that is basically for all real $x$....then your statement is totally wrong....I don't think the $(\frac{u}{v})'$ idea is good for admitting all values of $x$ in real.....so if possible please post another solution....we are waiting for that
This post has been edited 1 time. Last edited by Rohit-2006, Apr 15, 2025, 5:50 PM
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