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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)!

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[*]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
Inequalities
sqing   13
N 2 minutes ago by sqing
Let $ a,b,c\geq 0 ,a+b+c\leq 3. $ Prove that
$$a^2+b^2+c^2+ab +2ca+2bc +  abc \leq \frac{251}{27}$$$$ a^2+b^2+c^2+ab+2ca+2bc  + \frac{2}{5}abc  \leq \frac{4861}{540}$$$$ a^2+b^2+c^2+ab+2ca+2bc  + \frac{7}{20}abc  \leq \frac{2381411}{26460}$$
13 replies
sqing
Yesterday at 12:47 PM
sqing
2 minutes ago
Maximum value of function (with two variables)
Saucepan_man02   1
N 3 minutes ago by Saucepan_man02
If $f(\theta) = \min(|2x-7|+|x-4|+|x-2 -\sin \theta|)$, where $x, \theta \in \mathbb R$, then maximum value of $f(\theta)$.
1 reply
1 viewing
Saucepan_man02
17 minutes ago
Saucepan_man02
3 minutes ago
Geometry Finale: Incircles and concurrency
lminsl   174
N 43 minutes ago by LitleCabage0639
Source: IMO 2019 Problem 6
Let $I$ be the incentre of acute triangle $ABC$ with $AB\neq AC$. The incircle $\omega$ of $ABC$ is tangent to sides $BC, CA$, and $AB$ at $D, E,$ and $F$, respectively. The line through $D$ perpendicular to $EF$ meets $\omega$ at $R$. Line $AR$ meets $\omega$ again at $P$. The circumcircles of triangle $PCE$ and $PBF$ meet again at $Q$.

Prove that lines $DI$ and $PQ$ meet on the line through $A$ perpendicular to $AI$.

Proposed by Anant Mudgal, India
174 replies
lminsl
Jul 17, 2019
LitleCabage0639
43 minutes ago
Functional equations
mathematical-forest   0
an hour ago
Find all funtion $f:C\to C$, s.t.$\forall x \in C$
$$xf(x)=\overline{x} f(\overline{x})$$
0 replies
mathematical-forest
an hour ago
0 replies
cubefree divisibility
DottedCaculator   61
N an hour ago by sansgankrsngupta
Source: 2021 ISL N1
Find all positive integers $n\geq1$ such that there exists a pair $(a,b)$ of positive integers, such that $a^2+b+3$ is not divisible by the cube of any prime, and $$n=\frac{ab+3b+8}{a^2+b+3}.$$
61 replies
+1 w
DottedCaculator
Jul 12, 2022
sansgankrsngupta
an hour ago
It is given that $M=1+\frac12+\frac13+\frac14+\cdots+\frac{1}{23}=\frac{n}{23!},
Vulch   3
N 2 hours ago by mohabstudent1
It is given that $M=1+\frac12+\frac13+\frac14+\cdots+\frac{1}{23}=\frac{n}{23!},$ where $n$ is a natural number.What is the remainder when $n$ is divided by $13?$
3 replies
Vulch
Apr 9, 2025
mohabstudent1
2 hours ago
Cauchy and multiplicative function over a field extension
miiirz30   5
N 2 hours ago by AshAuktober
Source: 2025 Euler Olympiad, Round 2
Find all functions $f : \mathbb{Q}[\sqrt{2}] \to \mathbb{Q}[\sqrt{2}]$ such that for all $x, y \in \mathbb{Q}[\sqrt{2}]$,
$$
f(xy) = f(x)f(y) \quad \text{and} \quad f(x + y) = f(x) + f(y),
$$where $\mathbb{Q}[\sqrt{2}] = \{ a + b\sqrt{2} \mid a, b \in \mathbb{Q} \}$.

Proposed by Stijn Cambie, Belgium
5 replies
miiirz30
3 hours ago
AshAuktober
2 hours ago
Vieta's Relations
P162008   8
N 2 hours ago by mohabstudent1
If $\alpha,\beta$ and $\gamma$ are the roots of the cubic equation $x^3 - x^2 + 2x - 3 = 0.$
Evaluate $\sum_{cyc} \frac{\alpha^3 - 3}{\alpha^2 - 2}$
Is there any alternate approach except just bash
8 replies
P162008
Yesterday at 10:11 PM
mohabstudent1
2 hours ago
Find f
Redriver   6
N 2 hours ago by Unique_solver
Find all $: R \to R : \ \ f(x^2+f(y))=y+f^2(x)$
6 replies
Redriver
Jun 25, 2006
Unique_solver
2 hours ago
Circle
bilarev   2
N 2 hours ago by Blackbeam999
Let $k$ be a circle, $AB$ and $CD$ are parallel chords and $l$ is a
line from C, that intersects $AB$ in its middle point $L$ and $l\cap k=E$. $K$ is the middle of $DE$. Prove that $\angle AKE=\angle BKE.$
2 replies
bilarev
Oct 11, 2006
Blackbeam999
2 hours ago
Show that 2 triangles are bilogic
kosmonauten3114   0
2 hours ago
Source: My own
Given a scalene acute triangle $\triangle{ABC}$ with orthic triangle $\triangle{H_AH_BH_C}$, let $P_A$, $P_B$, $P_C$ be points such that $\triangle{AH_BH_C}\cup P_A \sim \triangle{H_ABH_C}\cup P_B \sim \triangle{H_AH_BC}\cup P_C$. Let $\ell_A$ be the trilinear polar of the polar conjugate of $P_A$ wrt $\triangle{ABC}$, and define $\ell_B$ and $\ell_C$ cyclically. Let $\triangle{A'B'C'}$ be the triangle bounded by $\ell_A$, $\ell_B$, $\ell_C$.
Show that $\triangle{ABC}$ and $\triangle{A'B'C'}$ are bilogic.
0 replies
kosmonauten3114
2 hours ago
0 replies
Interesting functions with iterations over integers
miiirz30   0
3 hours ago
Source: 2025 Euler Olympiad, Round 2
For any subset $S \subseteq \mathbb{Z}^+$, a function $f : S \to S$ is called interesting if the following two conditions hold:

1. There is no element $a \in S$ such that $f(a) = a$.
2. For every $a \in S$, we have $f^{f(a) + 1}(a) = a$ (where $f^{k}$ denotes the $k$-th iteration of $f$).

Prove that:
a) There exist infinitely many interesting functions $f : \mathbb{Z}^+ \to \mathbb{Z}^+$.

b) There exist infinitely many positive integers $n$ for which there is no interesting function
$$
f : \{1, 2, \ldots, n\} \to \{1, 2, \ldots, n\}.
$$
Proposed by Giorgi Kekenadze, Georgia
0 replies
miiirz30
3 hours ago
0 replies
Moving stones on an infinite row
miiirz30   0
3 hours ago
Source: 2025 Euler Olympiad, Round 2
We are given an infinite row of cells extending infinitely in both directions. Some cells contain one or more stones. The total number of stones is finite. At each move, the player performs one of the following three operations:

1. Take three stones from some cell, and add one stone to the cells located one cell to the left and one cell to the right, each skipping one cell in between.

2. Take two stones from some cell, and add one stone to the cell one cell to the left, skipping one cell and one stone to the adjacent cell to the right.

3. Take one stone from each of two adjacent cells, and add one stone to the cell to the right of these two cells.

The process ends when no moves are possible. Prove that the process always terminates and the final distribution of stones does not depend on the choices of moves made by the player.

IMAGE

Proposed by Luka Tsulaia, Georgia
0 replies
miiirz30
3 hours ago
0 replies
Alice, Bob and 6 boxes
Anulick   1
N 3 hours ago by RPCX
Source: SMMC 2024, B1
Alice has six boxes labelled 1 through 6. She secretly chooses exactly two of the boxes and places a coin inside each. Bob is trying to guess which two boxes contain the coins. Each time Bob guesses, he does so by tapping exactly two of the boxes. Alice then responds by telling him the total number of coins inside the two boxes that he tapped. Bob successfully finds the two coins when Alice responds with the number 2.

What is the smallest positive integer $n$ such that Bob can always find the two coins in at most $n$ guesses?
1 reply
Anulick
Oct 12, 2024
RPCX
3 hours ago
Absolute value
Silverfalcon   8
N Apr 22, 2025 by zhoujef000
This problem seemed to be too obvious.. And I think I"m wrong.. :D

Problem:

Consider the sequence $x_0, x_1, x_2,...x_{2000}$ of integers satisfying

\[x_0 = 0, |x_n| = |x_{n-1} + 1|\]

for $n = 1,2,...2000$.

Find the minimum value of the expression $|x_1 + x_2 + ... x_{2000}|$.

My idea

Pretty sure I'm wrong but where did I go wrong?
8 replies
Silverfalcon
Jun 27, 2005
zhoujef000
Apr 22, 2025
Absolute value
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Silverfalcon
5006 posts
#1 • 2 Y
Y by Adventure10, Mango247
This problem seemed to be too obvious.. And I think I"m wrong.. :D

Problem:

Consider the sequence $x_0, x_1, x_2,...x_{2000}$ of integers satisfying

\[x_0 = 0, |x_n| = |x_{n-1} + 1|\]

for $n = 1,2,...2000$.

Find the minimum value of the expression $|x_1 + x_2 + ... x_{2000}|$.

My idea

Pretty sure I'm wrong but where did I go wrong?
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Palytoxin
490 posts
#2 • 2 Y
Y by Adventure10, Mango247
yes wrong because check this out

$|x_1|=|x_0+1|=|1|$ and this means that $x_1$ can be $x_1=1$ or $x_1=-1$
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Silverfalcon
5006 posts
#3 • 2 Y
Y by Adventure10, Mango247
Ohh..

Then

I'm not sure if that makes the minimum though. No wonder it's the last question now..
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peeta
364 posts
#4 • 2 Y
Y by Adventure10, Mango247
well when u say every even will be 0 u can say for the odd $|x_n|=1$ therefore u can use 1 and -1 alternating coming to the minimum of 0, because there is sequence is periodic with the period 4, and the first 4 $x_n$ besides $x_0$ are 0 and they repeat themselves 250 times. also 0 is the smallest number possible, since $|x|\ge 0$
done :)
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JesusFreak197
1939 posts
#5 • 2 Y
Y by Adventure10, Mango247
Sweet, an Olympiad problem that I can actually solve! :P

Click to reveal hidden text
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K81o7
2417 posts
#6 • 2 Y
Y by Adventure10, Mango247
Peeta...there's a slight problem...
You can't go from 1 to 0...the thing about this problem is that $|x_n|\le|x_{n+1}|$ when $x_n$ is positive. In other words, you can't go from 1 to -1.
This one isn't quite as easy as it looks at first...
I'm thinking of one where the minimum is 12...
Basically you can start with 0, then go
-1, 0, 1, -2, -1, 0, 1, 2, -3, ...
going through sets of sizes which are an odd number each, and by the time you get to 22, you'll be at $x_1976$. 24 more numbers. Then, you go
-23, 22, -23, 22, -23...
But, if there's a way that 2000 - square number=multiple of 23 or 21, then the minimum is 0.
I'm sure there's a solution for that...
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JesusFreak197
1939 posts
#7 • 2 Y
Y by Adventure10, Mango247
Oh, you're right... by a more complicated set, you might be able to get it lower.
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Assassino9931
1362 posts
#8
Y by
Bump this
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zhoujef000
322 posts
#9
Y by
see 2006 AIME I P15 for a similar problem. (post #9 has a good solution)
This post has been edited 1 time. Last edited by zhoujef000, Apr 22, 2025, 7:47 PM
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