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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

Are you interested in working towards MATHCOUNTS and don’t know where to start? We have you covered! If you have taken Prealgebra, then you are ready for MATHCOUNTS/AMC 8 Basics. Already aiming for State or National MATHCOUNTS and harder AMC 8 problems? Then our MATHCOUNTS/AMC 8 Advanced course is for you.

Summer camps are starting next month at the Virtual Campus in math and language arts that are 2 - to 4 - weeks in duration. Spaces are still available - don’t miss your chance to have an enriching summer experience. 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)!

Be sure to mark your calendars for the following upcoming events:
[list][*]May 9th, 4:30pm PT/7:30pm ET, Casework 2: Overwhelming Evidence — A Text Adventure, a game where participants will work together to navigate the map, solve puzzles, and win! All are welcome.
[*]May 19th, 4:30pm PT/7:30pm ET, What's Next After Beast Academy?, designed for students finishing Beast Academy and ready for Prealgebra 1.
[*]May 20th, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 1 Math Jam, Problems 1 to 4, join the Canada/USA Mathcamp staff for this exciting Math Jam, where they discuss solutions to Problems 1 to 4 of the 2025 Mathcamp Qualifying Quiz!
[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/list]
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0 replies
jlacosta
May 1, 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
Difficult combinatorics problem
shactal   5
N 6 minutes ago by shactal
Can someone help me with this problem? Let $n\in \mathbb N^*$. We call a distribution the act of distributing the integers from $1$
to $n^2$ represented by tokens to players $A_1$ to $A_n$ so that they all have the same number of tokens in their urns.
We say that $A_i$ beats $A_j$ when, when $A_i$ and $A_j$ each draw a token from their urn, $A_i$ has a strictly greater chance of drawing a larger number than $A_j$. We then denote $A_i>A_j$. A distribution is said to be chicken-fox-viper when $A_1>A_2>\ldots>A_n>A_1$ What is $R(n)$
, the number of chicken-fox-viper distributions?
5 replies
shactal
Yesterday at 10:40 AM
shactal
6 minutes ago
My Unsolved Problem
ZeltaQN2008   1
N 9 minutes ago by Ash_the_Bash07
Let $\triangle ABC$ satisfy $AB<AC$. The circumcircle $(O)$ and the incircle $(I)$ of $\triangle ABC$ are tangent to the sides $AC,AB$ at $E,F$, respectively. The line $BI$ meets $EF$ at $M$ and intersects $AC$ at $P$, while the line $BO$ meets $CM$ at $Q$. Construct the common external tangent $\ell$ (different from $BC$) to the incircles of the triangles $PBC$ and $QBC$. Show that $\ell$ is parallel to the line $PQ$.
1 reply
ZeltaQN2008
12 minutes ago
Ash_the_Bash07
9 minutes ago
Point inside parallelogram
BigSams   21
N 16 minutes ago by Want-to-study-in-NTU-MATH
Source: Canadian Mathematical Olympiad - 1997 - Problem 4.
The point $O$ is situated inside the parallelogram $ABCD$ such that $\angle AOB+\angle COD=180^{\circ}$. Prove that $\angle OBC=\angle ODC$.
21 replies
BigSams
May 7, 2011
Want-to-study-in-NTU-MATH
16 minutes ago
Geometry
MathsII-enjoy   1
N 18 minutes ago by MathsII-enjoy
Given triangle $ABC$ inscribed in $(O)$ with $M$ being the midpoint of $BC$. The tangents at $B, C$ of $(O)$ intersect at $D$. Let $N$ be the projection of $O$ onto $AD$. On the perpendicular bisector of $BC$, take a point $K$ that is not on $(O)$ and different from M. Circle $(KBC)$ intersects $AK$ at $F$. Lines $NF$ and $AM$ intersect at $E$. Prove that $AEF$ is an isosceles triangle.
1 reply
MathsII-enjoy
May 15, 2025
MathsII-enjoy
18 minutes ago
Probably a good lemma
Zavyk09   5
N 26 minutes ago by Orzify
Source: found when solving exercises
Let $ABC$ be a triangle with circumcircle $\omega$. Arbitrary points $E, F$ on $AC, AB$ respectively. Circumcircle $\Omega$ of triangle $AEF$ intersects $\omega$ at $P \ne A$. $BE$ intersects $CF$ at $I$. $PI$ cuts $\Omega$ and $\omega$ at $K, L$ respectively. Construct parallelogram $KFRE$. Prove that $A, R, L$ are collinear.
5 replies
Zavyk09
Yesterday at 12:50 PM
Orzify
26 minutes ago
D1033 : A problem of probability for dominoes 3*1
Dattier   1
N an hour ago by Dattier
Source: les dattes à Dattier
Let $G$ a grid of 9*9, we choose a little square in $G$ of this grid three times, we can choose three times the same.

What the probability of cover with 3*1 dominoes this grid removed by theses little squares (one, two or three) ?
1 reply
Dattier
May 15, 2025
Dattier
an hour ago
Two perpendiculars
jayme   2
N an hour ago by jayme
Source: Own?
Dear Mathlinkers,

1. ABC a triangle
2. 0 the circumcircle
3. D the pole of BC wrt 0
4. B', C' the symmetrics of B, C wrt AC, AB
5. 1b, 1c the circumcircles of the triangles BB'D, CC'D
6. J the center of 1b
7. V the second point of intersection of DJ and 1c.

Prove : CV is perpendicular to BC.

Sincerely
Jean-Louis
2 replies
jayme
5 hours ago
jayme
an hour ago
IMO 2009, Problem 3
orl   52
N an hour ago by N3bula
Source: IMO 2009, Problem 3
Suppose that $ s_1,s_2,s_3, \ldots$ is a strictly increasing sequence of positive integers such that the sub-sequences \[s_{s_1},\, s_{s_2},\, s_{s_3},\, \ldots\qquad\text{and}\qquad s_{s_1+1},\, s_{s_2+1},\, s_{s_3+1},\, \ldots\] are both arithmetic progressions. Prove that the sequence $ s_1, s_2, s_3, \ldots$ is itself an arithmetic progression.

Proposed by Gabriel Carroll, USA
52 replies
orl
Jul 15, 2009
N3bula
an hour ago
Find all functions $f$: \(\mathbb{R}\) \(\rightarrow\) \(\mathbb{R}\) such : $f(
guramuta   2
N an hour ago by GreekIdiot
Find all functions $f$: \(\mathbb{R}\) \(\rightarrow\) \(\mathbb{R}\) such :
$f(x+yf(x)) + f(xf(y)-y) = f(x) - f(y) + 2xy$
2 replies
guramuta
Yesterday at 2:18 PM
GreekIdiot
an hour ago
Another triangle
Rushil   14
N 2 hours ago by SomeonecoolLovesMaths
Source: Indian RMO 1991 Problem 1
Let $P$ be an interior point of a triangle $ABC$ and $AP,BP,CP$ meet the sides $BC,CA,AB$ in $D,E,F$ respectively. Show that \[ \frac{AP}{PD} = \frac{AF}{FB} + \frac{AE}{EC}.  \]
Remark
14 replies
Rushil
Oct 15, 2005
SomeonecoolLovesMaths
2 hours ago
13rd ibmo - rep. dominicana 1998/q2.
carlosbr   6
N 2 hours ago by fearsum_fyz
Source: Spanish Communities
The circumference inscribed on the triangle $ABC$ is tangent to the sides $BC$, $CA$ and $AB$ on the points $D$, $E$ and $F$, respectively. $AD$ intersect the circumference on the point $Q$. Show that the line $EQ$ meet the segment $AF$ at its midpoint if and only if $AC=BC$.
6 replies
carlosbr
Apr 16, 2006
fearsum_fyz
2 hours ago
Inspired by old results
sqing   1
N 3 hours ago by sqing
Source: Own
Let $ a, b\geq 0, a+b=2. $ Prove that
$$\frac {24}{25} < \frac {1}{a^3 + 1 + ab}+\frac {1}{b^3 +1 + ab} +\frac {1}{a^3 + b^3 + ab} \leq \frac {89}{72}$$Let $ a, b\geq 0,  a+b+ab=3. $ Prove that
$$\frac {4}{5} < \frac {1}{a^3 + 1 + ab}+\frac {1}{b^3 +1 + ab} +\frac {1}{a^3 + b^3 + ab} \leq \frac {811}{756}$$Let $ a, b\geq 0,  a+b+ab=2. $ Prove that
$$\frac {23}{20} < \frac {1}{a^3 + 1 + ab}+\frac {1}{b^3 +1 + ab} +\frac {1}{a^3 + b^3 + ab} \leq \frac {404+291\sqrt{3}}{506}$$
1 reply
sqing
3 hours ago
sqing
3 hours ago
RMM 2013 Problem 6
dr_Civot   15
N 3 hours ago by N3bula
A token is placed at each vertex of a regular $2n$-gon. A move consists in choosing an edge of the $2n$-gon and swapping the two tokens placed at the endpoints of that edge. After a finite number of moves have been performed, it turns out that every two tokens have been swapped exactly once. Prove that some edge has never been chosen.
15 replies
dr_Civot
Mar 3, 2013
N3bula
3 hours ago
3-variable inequality with min(ab,bc,ca)>=1
mathwizard888   72
N 3 hours ago by math-olympiad-clown
Source: 2016 IMO Shortlist A1
Let $a$, $b$, $c$ be positive real numbers such that $\min(ab,bc,ca) \ge 1$. Prove that $$\sqrt[3]{(a^2+1)(b^2+1)(c^2+1)} \le \left(\frac{a+b+c}{3}\right)^2 + 1.$$
Proposed by Tigran Margaryan, Armenia
72 replies
mathwizard888
Jul 19, 2017
math-olympiad-clown
3 hours ago
construct triangle
rogue   1
N Sep 10, 2008 by mr.danh
Source: Ukrainian journal contest, problem 329, by Grygoriy Filippovskyy
Construct triangle $ ABC$ given points $ O_A$ and $ O_B,$ which are symmetric to its circumcenter $ O$ with respect to $ BC$ and $ AC,$ and the straight line $ h_A,$ which contains its altitude to $ BC.$
1 reply
rogue
Sep 9, 2008
mr.danh
Sep 10, 2008
construct triangle
G H J
Source: Ukrainian journal contest, problem 329, by Grygoriy Filippovskyy
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rogue
554 posts
#1 • 2 Y
Y by Adventure10, Mango247
Construct triangle $ ABC$ given points $ O_A$ and $ O_B,$ which are symmetric to its circumcenter $ O$ with respect to $ BC$ and $ AC,$ and the straight line $ h_A,$ which contains its altitude to $ BC.$
Z K Y
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mr.danh
635 posts
#2 • 2 Y
Y by Adventure10, Mango247
rogue wrote:
Construct triangle $ ABC$ given points $ O_A$ and $ O_B,$ which are symmetric to its circumcenter $ O$ with respect to $ BC$ and $ AC,$ and the straight line $ h_A,$ which contains its altitude to $ BC.$
The perpendicular bisector of $ O_AO_B$ meets the line $ h_A$ at the orthocenter H. The circle through H centered $ O_A$ meets the circle through H centered $ O_B$ at C. The circle $ (O_A)$ meets the perp line from C to $ h_A$ at B.
Z K Y
N Quick Reply
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