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k a April Highlights and 2025 AoPS Online Class Information
jlacosta   0
Apr 2, 2025
Spring is in full swing and summer is right around the corner, what are your plans? At AoPS Online our schedule has new classes starting now through July, so be sure to keep your skills sharp and be prepared for the Fall school year! Check out the schedule of upcoming classes below.

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Looking for summer camps in math and language arts? Be sure to check out the video-based summer camps offered at the Virtual Campus that are 2- to 4-weeks in duration. There are middle and high school competition math camps as well as Math Beasts camps that review key topics coupled with fun explorations covering areas such as graph theory (Math Beasts Camp 6), cryptography (Math Beasts Camp 7-8), and topology (Math Beasts Camp 8-9)!

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[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
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0 replies
jlacosta
Apr 2, 2025
0 replies
k i Adding contests to the Contest Collections
dcouchman   1
N Apr 5, 2023 by v_Enhance
Want to help AoPS remain a valuable Olympiad resource? Help us add contests to AoPS's Contest Collections.

Find instructions and a list of contests to add here: https://artofproblemsolving.com/community/c40244h1064480_contests_to_add
1 reply
dcouchman
Sep 9, 2019
v_Enhance
Apr 5, 2023
k i Zero tolerance
ZetaX   49
N May 4, 2019 by NoDealsHere
Source: Use your common sense! (enough is enough)
Some users don't want to learn, some other simply ignore advises.
But please follow the following guideline:


To make it short: ALWAYS USE YOUR COMMON SENSE IF POSTING!
If you don't have common sense, don't post.


More specifically:

For new threads:


a) Good, meaningful title:
The title has to say what the problem is about in best way possible.
If that title occured already, it's definitely bad. And contest names aren't good either.
That's in fact a requirement for being able to search old problems.

Examples:
Bad titles:
- "Hard"/"Medium"/"Easy" (if you find it so cool how hard/easy it is, tell it in the post and use a title that tells us the problem)
- "Number Theory" (hey guy, guess why this forum's named that way¿ and is it the only such problem on earth¿)
- "Fibonacci" (there are millions of Fibonacci problems out there, all posted and named the same...)
- "Chinese TST 2003" (does this say anything about the problem¿)
Good titles:
- "On divisors of a³+2b³+4c³-6abc"
- "Number of solutions to x²+y²=6z²"
- "Fibonacci numbers are never squares"


b) Use search function:
Before posting a "new" problem spend at least two, better five, minutes to look if this problem was posted before. If it was, don't repost it. If you have anything important to say on topic, post it in one of the older threads.
If the thread is locked cause of this, use search function.

Update (by Amir Hossein). The best way to search for two keywords in AoPS is to input
[code]+"first keyword" +"second keyword"[/code]
so that any post containing both strings "first word" and "second form".


c) Good problem statement:
Some recent really bad post was:
[quote]$lim_{n\to 1}^{+\infty}\frac{1}{n}-lnn$[/quote]
It contains no question and no answer.
If you do this, too, you are on the best way to get your thread deleted. Write everything clearly, define where your variables come from (and define the "natural" numbers if used). Additionally read your post at least twice before submitting. After you sent it, read it again and use the Edit-Button if necessary to correct errors.


For answers to already existing threads:


d) Of any interest and with content:
Don't post things that are more trivial than completely obvious. For example, if the question is to solve $x^{3}+y^{3}=z^{3}$, do not answer with "$x=y=z=0$ is a solution" only. Either you post any kind of proof or at least something unexpected (like "$x=1337, y=481, z=42$ is the smallest solution). Someone that does not see that $x=y=z=0$ is a solution of the above without your post is completely wrong here, this is an IMO-level forum.
Similar, posting "I have solved this problem" but not posting anything else is not welcome; it even looks that you just want to show off what a genius you are.

e) Well written and checked answers:
Like c) for new threads, check your solutions at least twice for mistakes. And after sending, read it again and use the Edit-Button if necessary to correct errors.



To repeat it: ALWAYS USE YOUR COMMON SENSE IF POSTING!


Everything definitely out of range of common sense will be locked or deleted (exept for new users having less than about 42 posts, they are newbies and need/get some time to learn).

The above rules will be applied from next monday (5. march of 2007).
Feel free to discuss on this here.
49 replies
ZetaX
Feb 27, 2007
NoDealsHere
May 4, 2019
Monic Polynomial
IstekOlympiadTeam   22
N 7 minutes ago by zuat.e
Source: Romanian Masters 2017 D1 P2
Determine all positive integers $n$ satisfying the following condition: for every monic polynomial $P$ of degree at most $n$ with integer coefficients, there exists a positive integer $k\le n$ and $k+1$ distinct integers $x_1,x_2,\cdots ,x_{k+1}$ such that \[P(x_1)+P(x_2)+\cdots +P(x_k)=P(x_{k+1})\].

Note. A polynomial is monic if the coefficient of the highest power is one.
22 replies
IstekOlympiadTeam
Feb 25, 2017
zuat.e
7 minutes ago
Transforming a grid to another
Severus   3
N 8 minutes ago by HoRI_DA_GRe8
Source: STEMS 2021 Cat B P5
Sheldon was really annoying Leonard. So to keep him quiet, Leonard decided to do something. He gave Sheldon the following grid

$\begin{tabular}{|c|c|c|c|c|c|}
\hline
1 & 1 & 1 & 1 & 1 & 0\\ 
\hline
1 & 1 & 1 & 1 & 0 & 0\\ 
\hline
1 & 1 & 1 & 0 & 0 & 0\\ 
\hline
1 & 1 & 0 & 0 & 0 & 1\\ 
\hline
1 & 0 & 0 & 0 & 1 & 0\\
\hline
0 & 0 & 0 & 1 & 0 & 0\\
\hline
\end{tabular}$

and asked him to transform it to the new grid below

$\begin{tabular}{|c|c|c|c|c|c|}
\hline
1 & 2 & 18 &24 &28 &30\\
\hline
21 & 3 & 4 &16 &22 &26\\
\hline
23 &19 & 5 & 6 &14 &20\\
\hline
32 &25 &17 & 7 & 8 &12\\
\hline
33 &34 &27 &15 & 9 &10\\
\hline
35 &31 &36 &29 &13 &11\\
\hline
\end{tabular}$

by only applying the following algorithm:

$\bullet$ At each step, Sheldon must choose either two rows or two columns.

$\bullet$ For two columns $c_1, c_2$, if $a,b$ are entries in $c_1, c_2$ respectively, then we say that $a$ and $b$ are corresponding if they belong to the same row. Similarly we define corresponding entries of two rows. So for Sheldon's choice, if two corresponding entries have the same parity, he should do nothing to them, but if they have different parities, he should add 1 to both of them.

Leonard hoped this would keep Sheldon occupied for some time, but Sheldon immediately said, "But this is impossible!". Was Sheldon right? Justify.
3 replies
Severus
Jan 24, 2021
HoRI_DA_GRe8
8 minutes ago
D1010 : How it is possible ?
Dattier   16
N 12 minutes ago by Dattier
Source: les dattes à Dattier
Is it true that$$\forall n \in \mathbb N^*, (24^n \times B \mod A) \mod 2 = 0 $$?

A=1728400904217815186787639216753921417860004366580219212750904
024377969478249664644267971025952530803647043121025959018172048
336953969062151534282052863307398281681465366665810775710867856
720572225880311472925624694183944650261079955759251769111321319
421445397848518597584590900951222557860592579005088853698315463
815905425095325508106272375728975

B=2275643401548081847207782760491442295266487354750527085289354
965376765188468052271190172787064418854789322484305145310707614
546573398182642923893780527037224143380886260467760991228567577
953725945090125797351518670892779468968705801340068681556238850
340398780828104506916965606659768601942798676554332768254089685
307970609932846902
16 replies
Dattier
Mar 10, 2025
Dattier
12 minutes ago
EGMO Genre Predictions
ohiorizzler1434   23
N 30 minutes ago by ItsBesi
Everybody, with EGMO upcoming, what are you predictions for the problem genres?


Personally I predict: predict
23 replies
ohiorizzler1434
Mar 28, 2025
ItsBesi
30 minutes ago
quadratic with at least 1 roots
giangtruong13   0
an hour ago
Find $m$ to satisfy that the equation $x^2+mx-1=0$ has at least 1 roots $\leq -2$
0 replies
giangtruong13
an hour ago
0 replies
All numbers occur exactly once
Ankoganit   17
N an hour ago by bin_sherlo
Source: St. Petersburg Olympiad 2015, 2nd Round, Grade 9, also known as Yellowstone Permutation
A sequence of integers is defined as follows: $a_1=1,a_2=2,a_3=3$ and for $n>3$, $$a_n=\textsf{The smallest integer not occurring earlier, which is relatively prime to }a_{n-1}\textsf{ but not relatively prime to }a_{n-2}.$$Prove that every natural number occurs exactly once in this sequence.

M. Ivanov
17 replies
Ankoganit
Sep 24, 2016
bin_sherlo
an hour ago
Geometry
MathsII-enjoy   0
2 hours ago
Given triangle $ABC$ inscribed in $(O)$, $S$ is the midpoint of arc $BAC$ of $(O)$. The perpendicular bisector $BO$ intersects $BS$ at $I$. $(I;IB)$ intersects $AB$ at $U$ different from $B$. $H$ is the orthocenter of triangle $ABC$. Prove that $UH$ = $US$
0 replies
MathsII-enjoy
2 hours ago
0 replies
Find x such that x^4+x^3+x^2+x+1 is perfect square (old)
Amir Hossein   6
N 2 hours ago by zhoujef000
Find all numbers $x \in \mathbb Z$ for which the number
\[x^4 + x^3 + x^2 + x + 1\]
is a perfect square.
6 replies
Amir Hossein
Oct 3, 2010
zhoujef000
2 hours ago
Number Theory Chain!
JetFire008   54
N 2 hours ago by JetFire008
I will post a question and someone has to answer it. Then they have to post a question and someone else will answer it and so on. We can only post questions related to Number Theory and each problem should be more difficult than the previous. Let's start!

Question 1
54 replies
JetFire008
Apr 7, 2025
JetFire008
2 hours ago
Divisibility NT FE
CHESSR1DER   7
N 2 hours ago by CHESSR1DER
Source: Own
Find all functions $f$ $N \iff N$ such for any $a,b$:
$(a+b)|a^{f(b)} + b^{f(a)}$.
7 replies
CHESSR1DER
Yesterday at 7:07 PM
CHESSR1DER
2 hours ago
Parallelograms and concyclicity
Lukaluce   25
N 2 hours ago by kotmhn
Source: EGMO 2025 P4
Let $ABC$ be an acute triangle with incentre $I$ and $AB \neq AC$. Let lines $BI$ and $CI$ intersect the circumcircle of $ABC$ at $P \neq B$ and $Q \neq C$, respectively. Consider points $R$ and $S$ such that $AQRB$ and $ACSP$ are parallelograms (with $AQ \parallel RB, AB \parallel QR, AC \parallel SP$, and $AP \parallel CS$). Let $T$ be the point of intersection of lines $RB$ and $SC$. Prove that points $R, S, T$, and $I$ are concyclic.
25 replies
Lukaluce
Yesterday at 10:59 AM
kotmhn
2 hours ago
Weird Inequality Problem
Omerking   3
N 2 hours ago by Primeniyazidayi
Following inequality is given:
$$3\geq ab+bc+ca\geq \dfrac{1}{3}$$Find the range of values that can be taken by :
$1)a+b+c$
$2)abc$

Where $a,b,c$ are positive reals.
3 replies
Omerking
Today at 8:56 AM
Primeniyazidayi
2 hours ago
Injective arithmetic comparison
adityaguharoy   5
N 3 hours ago by vsamc
Source: Own .. probably own
Show or refute :
For every injective function $f: \mathbb{N} \to \mathbb{N}$ there are elements $a,b,c$ in an arithmetic progression in the order $a<b<c$ such that $f(a)<f(b)<f(c)$ .
5 replies
adityaguharoy
Jan 16, 2017
vsamc
3 hours ago
Divisibility of 121
kalra   1
N 3 hours ago by maxamc
Source: Own.
$5^{11m}+8^{11m}+11^{11m}+14^{11m}+17^{11m}+20^{11m}+23^{11m}+26^{11m}+29^{11m}+32^{11m}+35^{11m}$ would be divisible by $121$ for any integer values of $m$, provided $10$ is not a factor of $m$. How to prove this?
1 reply
kalra
Jun 11, 2022
maxamc
3 hours ago
Similar triangles ACD, AEF, AMN
Pentakratie   2
N Sep 24, 2013 by jayme
Source: German Mathematical Competition BWM 2005, 2nd round, problem
Two circles $k_1$ and $k_2$ intersect at two points $A$ and $B$. Some line through the point $B$ meets the circle $k_1$ at a point $C$ (apart from $B$), and the circle $k_2$ at a point $E$ (apart from $B$). Another line through the point $B$ meets the circle $k_1$ at a point $D$ (apart from $B$), and the circle $k_2$ at a point $F$ (apart from $B$). Assume that the point $B$ lies between the points $C$ and $E$ and between the points $D$ and $F$.

Finally, let $M$ and $N$ be the midpoints of the segments $CE$ and $DF$.

Prove that the triangles $ACD$, $AEF$ and $AMN$ are similar to each other.
2 replies
Pentakratie
Sep 1, 2005
jayme
Sep 24, 2013
Similar triangles ACD, AEF, AMN
G H J
Source: German Mathematical Competition BWM 2005, 2nd round, problem
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Pentakratie
25 posts
#1 • 2 Y
Y by Adventure10, Mango247
Two circles $k_1$ and $k_2$ intersect at two points $A$ and $B$. Some line through the point $B$ meets the circle $k_1$ at a point $C$ (apart from $B$), and the circle $k_2$ at a point $E$ (apart from $B$). Another line through the point $B$ meets the circle $k_1$ at a point $D$ (apart from $B$), and the circle $k_2$ at a point $F$ (apart from $B$). Assume that the point $B$ lies between the points $C$ and $E$ and between the points $D$ and $F$.

Finally, let $M$ and $N$ be the midpoints of the segments $CE$ and $DF$.

Prove that the triangles $ACD$, $AEF$ and $AMN$ are similar to each other.
Z K Y
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ThAzN1
867 posts
#2 • 2 Y
Y by Adventure10, Mango247
First, $\triangle ACD \sim \triangle AEF$ follows from

$\angle CAD = \angle CBD = \angle FBE = \angle FAE,$
$\angle ACD = \pi - \angle ABD = \angle ABF = \angle AEF.$

Now, note that $\triangle ACE \sim \triangle ADF$ because

$\angle ACE = \angle ACB = \angle ADB = \angle ADF,$
$\angle AEC = \angle AEB = \angle AFB = \angle AFB.$

Thus, $\triangle ACM \sim \triangle ADN$ and we have

$\frac{AM}{AN} = \frac{AC}{AD}.$

Additionally, $\triangle ACE$ is taken to $\triangle ADF$ by a spiral similarity about $A$, with rotation angle $\angle CAD$, ratio $AD/AC$ so $M$ goes to $N$ under this spiral similarity and $\angle MAN = \angle CAD$, so the result follows...
Z K Y
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jayme
9775 posts
#3 • 2 Y
Y by Adventure10, Mango247
Dear Mathlinkers,
according to the midcircle theorem, A, B, M and N are concyclic.
By an angle chasing, we are done.
Sincerely
Jean-Louis
Z K Y
N Quick Reply
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