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k a August Highlights and 2025 AoPS Online Class Information
jwelsh   0
Aug 1, 2025
CONGRATULATIONS to all the competitors at this year’s International Mathematical Olympiad (IMO)! The US Team took second place with 5 gold medals and 1 silver - we are proud to say that each member of the 2025 IMO team has participated in an AoPS WOOT (Worldwide Online Olympiad Training) class!

"As a parent, I'm deeply grateful to AoPS. Tiger has taken very few math courses outside of AoPS, except for a local Math Circle that doesn't focus on Olympiad math. AoPS has been one of the most important resources in his journey. Without AoPS, Tiger wouldn't be where he is today — especially considering he's grown up in a family with no STEM background at all."
— Doreen Dai, parent of IMO US Team Member Tiger Zhang

Interested to learn more about our WOOT programs? Check out the course page here or join a Free Scheduled Info Session. Early bird pricing ends August 19th!:
CodeWOOT Code Jam - Monday, August 11th
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PhysicsWOOT Physics Jam - Thursday, August 14th
MathWOOT Math Jam - Friday, August 15th

There is still time to enroll in our last wave of summer camps that start in August at the Virtual Campus, our video-based platform, for math and language arts! From Math Beasts Camp 6 (Prealgebra Prep) to AMC 10/12 Prep, you can find an informative 2-week camp before school starts. Plus, our math camps don’t have homework and cover cool enrichment topics like graph theory. Our language arts courses will build the foundation for next year’s challenges, such as Language Arts Triathlon for levels 5-6 and Academic Essay Writing for high school students.

Lastly, Fall is right around the corner! You can plan your Fall schedule now with classes at either AoPS Online, AoPS Academy Virtual Campus, or one of our AoPS Academies around the US. We’ve opened new Academy locations in San Mateo, CA, Pasadena, CA, Saratoga, CA, Johns Creek, GA, Northbrook, IL, and Upper West Side (NYC), New York.

Our full course list for upcoming classes is below:
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0 replies
jwelsh
Aug 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
Knight Yuri
RaymondZhu   17
N 7 minutes ago by simpleK
Source: ISL 2024 C3
Let $n$ be a positive integer. There are $2n$ knights sitting at a round table. They consist of $n$ pairs of partners, each pair of which wishes to shake hands. A pair can shake hands only when next to each other. Every minute, one pair of adjacent knights swaps places. Find the minimum number of exchanges of adjacent knights such that, regardless of the initial arrangement, every knight can meet her partner and shake hands at some time.
17 replies
RaymondZhu
Jul 16, 2025
simpleK
7 minutes ago
Israel 2023(winter camp, team competition, p.6)
arqady   6
N 17 minutes ago by Rhapsodies_pro
Let $ABCD$ be a cyclic quadrilateral, $AB=a$, $BC=b$, $CD=c$, $DA=d$, $AC=e$ and $BD=f.$ Prove that:
$$\frac{1}{ab}+\frac{1}{bc}+\frac{1}{cd}+\frac{1}{da}\geq4\left(\frac{1}{e^2}+\frac{1}{f^2}\right)$$
6 replies
arqady
Jan 31, 2023
Rhapsodies_pro
17 minutes ago
n-variable trigonometry inequality
VoidMutsumi   1
N 28 minutes ago by VoidMutsumi
Source: Own problem
Given the integer $n\geqslant 3$, let nonnegative reals $x_1,\cdots,x_n$ satisfy $\displaystyle\sum_{i=1}^n x_i = \frac{\pi}2$. Prove:
$$
\sum_{i=1}^n \frac1{1-\sin(x_i)\sin(x_{i+1})} \leqslant n+1,
$$where $x_{n+1} = x_1$. (The equality holds if $x_1=x_2=\dfrac{\pi}4$ and other $x_i$ being 0.)
1 reply
VoidMutsumi
29 minutes ago
VoidMutsumi
28 minutes ago
Find all functions
aktyw19   6
N an hour ago by P0tat0b0y
Find all functions $f:\mathbb{R} \rightarrow \mathbb{R}$ such that $f(x+f(y))=f(y+f(x))$
6 replies
aktyw19
Apr 30, 2011
P0tat0b0y
an hour ago
A Solution Of The Collatz Conjecture Problem(v14)
duanby163   27
N an hour ago by littleduckysteve
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27 replies
duanby163
Mar 24, 2024
littleduckysteve
an hour ago
Οn f(f(f(x)))=-x
GreekIdiot   6
N an hour ago by TimeDependentSubset
I was playing around for a bit and found some nontrivial functions such that $f(f(f(x)))=-x \: \forall \: x \in \Delta$, where $f:\Delta \to \mathbb R$. This made me wonder, does there exist a nice family of solutions describing all of them?
6 replies
GreekIdiot
Yesterday at 9:22 PM
TimeDependentSubset
an hour ago
Junior Balkan Mathematical Olympiad 2024- P2
Lukaluce   21
N an hour ago by Namura
Source: JBMO 2024
Let $ABC$ be a triangle such that $AB < AC$. Let the excircle opposite to A be tangent to the lines $AB, AC$, and $BC$ at points $D, E$, and $F$, respectively, and let $J$ be its centre. Let $P$ be a point on the side $BC$. The circumcircles of the triangles $BDP$ and $CEP$ intersect for the second time at $Q$. Let $R$ be the foot of the perpendicular from $A$ to the line $FJ$. Prove that the points $P, Q$, and $R$ are collinear.

(The excircle of a triangle $ABC$ opposite to $A$ is the circle that is tangent to the line segment $BC$, to the ray $AB$ beyond $B$, and to the ray $AC$ beyond $C$.)

Proposed by Bozhidar Dimitrov, Bulgaria
21 replies
Lukaluce
Jun 27, 2024
Namura
an hour ago
P lies in diagonal CE of ABCDE iff (BCD)+(ADE)=(ABD)+(ABP)
parmenides51   11
N an hour ago by mpcnotnpc
Source: IMO 2019 SL G5
Let $ABCDE$ be a convex pentagon with $CD= DE$ and $\angle EDC \ne 2 \cdot \angle ADB$.
Suppose that a point $P$ is located in the interior of the pentagon such that $AP =AE$ and $BP= BC$.
Prove that $P$ lies on the diagonal $CE$ if and only if area $(BCD)$ + area $(ADE)$ = area $(ABD)$ + area $(ABP)$.

(Hungary)
11 replies
parmenides51
Sep 22, 2020
mpcnotnpc
an hour ago
The line OI is parallel to one of the side of a triangle
Pindp   0
2 hours ago
Source: Own
Dedicated to the birthday of my teacher, Le Viet An
Let $ABC$ be a triangle with incenter $I$ and circumcenter $O$, such that $OI\parallel BC$. Let $M$ be the midpoint of $BC$, and let $E$ and $F$ be the points where $OI$ intersects $CA$ and $AB$, respectively. A line passing through $M$ and perpendicular to $AI$ intersects $IB$ and $IC$ at $Y$ and $Z$, respectively. Prove that the circle symmetric to the circumcircle of $\triangle IYZ$ wrt $YZ$ is tangent to the circumcircle of $\triangle AEF$.
0 replies
Pindp
2 hours ago
0 replies
Functional Geometry
naman12   12
N 2 hours ago by YaoAOPS
Source: 2019 ISL G8
Let $\mathcal L$ be the set of all lines in the plane and let $f$ be a function that assigns to each line $\ell\in\mathcal L$ a point $f(\ell)$ on $\ell$. Suppose that for any point $X$, and for any three lines $\ell_1,\ell_2,\ell_3$ passing through $X$, the points $f(\ell_1),f(\ell_2),f(\ell_3)$, and $X$ lie on a circle.
Prove that there is a unique point $P$ such that $f(\ell)=P$ for any line $\ell$ passing through $P$.

Australia
12 replies
naman12
Sep 22, 2020
YaoAOPS
2 hours ago
sum sqrt(a+3b+2/c) inequality with a+b+c=3
jasperE3   5
N 2 hours ago by lbh_qys
Source: IMOC 2017 A6
Show that for all positive reals $a,b,c$ with $a+b+c=3$,
$$\sum_{\text{cyc}}\sqrt{a+3b+\frac2c}\ge3\sqrt6.$$
5 replies
jasperE3
Aug 12, 2021
lbh_qys
2 hours ago
A tree with k edges
Omid Hatami   11
N 2 hours ago by john0512
Source: Iran TST 2008
Suppose that $ T$ is a tree with $ k$ edges. Prove that the $ k$-dimensional cube can be partitioned to graphs isomorphic to $ T$.
11 replies
Omid Hatami
May 20, 2008
john0512
2 hours ago
Steiner line and isogonal lines
flower417477   3
N 2 hours ago by flower417477
$\odot O$ is the circumcircle of $\triangle ABC$,$H$ is the orthocenter of $\triangle ABC$
$D$ is an arbitrary point on $\odot O$
$E$ is the reflection point of $D$ wrt $BC$,$EH$ meet $OD$ at $F$.
$K$ is the reflection point of $A$ wrt $OH$.
$P$ is a point on $\odot O$ such that $PK$ is parallel to $BC$,$Q$ is a point on $OH$ such that $PQ$ is parallel to $EH$.
$N$ is the circumcenter of $\triangle PQK$
Prove that $AF,AN$ is a pair of isogonal lines wrt $\angle BAC$
3 replies
flower417477
Jul 18, 2025
flower417477
2 hours ago
Sequence of Rational Numbers
v_Enhance   15
N 2 hours ago by dolphinday
Source: USA TSTST 2012, Problem 5
A rational number $x$ is given. Prove that there exists a sequence $x_0, x_1, x_2, \ldots$ of rational numbers with the following properties:
(a) $x_0=x$;
(b) for every $n\ge1$, either $x_n = 2x_{n-1}$ or $x_n = 2x_{n-1} + \textstyle\frac{1}{n}$;
(c) $x_n$ is an integer for some $n$.
15 replies
v_Enhance
Jul 19, 2012
dolphinday
2 hours ago
A second final attempt to make a combinatorics problem
JARP091   2
N May 29, 2025 by JARP091
Source: At the time of writing this problem I do not know the source if any
Arthur Morgan is playing a game.

He has $n$ eggs, each with a hardness value $k_1, k_2, \dots, k_n$, where $\{k_1, k_2, \dots, k_n\}$ is a permutation of the set $\{1, 2, \dots, n\}$. He is throwing the eggs from an $m$-floor building.

When the $i$-th egg is dropped from the $j$-th floor, its new hardness becomes
\[
\left\lfloor \frac{k_i}{j+1} \right\rfloor.
\]If $\left\lfloor \frac{k_i}{j+1} \right\rfloor = 0$, then the egg breaks and cannot be used again.

Arthur can drop each egg from a particular floor at most once.
For which values of $n$ and $m$ can Arthur always determine the correct ordering of the eggs according to their initial hardness values?
Note: The problem might be wrong or too easy
2 replies
JARP091
May 25, 2025
JARP091
May 29, 2025
A second final attempt to make a combinatorics problem
G H J
Source: At the time of writing this problem I do not know the source if any
The post below has been deleted. Click to close.
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JARP091
144 posts
#1
Y by
Arthur Morgan is playing a game.

He has $n$ eggs, each with a hardness value $k_1, k_2, \dots, k_n$, where $\{k_1, k_2, \dots, k_n\}$ is a permutation of the set $\{1, 2, \dots, n\}$. He is throwing the eggs from an $m$-floor building.

When the $i$-th egg is dropped from the $j$-th floor, its new hardness becomes
\[
\left\lfloor \frac{k_i}{j+1} \right\rfloor.
\]If $\left\lfloor \frac{k_i}{j+1} \right\rfloor = 0$, then the egg breaks and cannot be used again.

Arthur can drop each egg from a particular floor at most once.
For which values of $n$ and $m$ can Arthur always determine the correct ordering of the eggs according to their initial hardness values?
Note: The problem might be wrong or too easy
This post has been edited 1 time. Last edited by JARP091, May 25, 2025, 2:46 PM
Reason: Wrongly LaTeXted
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
JARP091
144 posts
#2
Y by
Bump for this problem
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
JARP091
144 posts
#3
Y by
Drop something from 1, if it breaks then its 0

if it doesnt break, it is currently 1, we have one more one, and we have a number we are trying to find out

we cant drop the number we are interested in from floor 1, otherwise we lose information

hence drop another egg from floor 2, if it doesnt break, it was 3, we started with a 2, and ther last egg is 1, if it breaks, then we either dropped a 1, or we dropped a 2, and so the possible outputs are (1,0,2) (1,0,3) (1,0,1), now we cant figure out what state the last egg is in, so it is impossible.

For n $>$ 3, n = 3 is a subproblem that cannot be solved.

Hence only possible solutions are:

i) n = 1, m $\geq$ 1

ii) n = 2, m $\geq$ 2
Z K Y
N Quick Reply
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