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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.

WOOT early bird pricing is in effect, don’t miss out! If you took MathWOOT Level 2 last year, no worries, it is all new problems this year! Our Worldwide Online Olympiad Training program is for high school level competitors. AoPS designed these courses to help our top students get the deep focus they need to succeed in their specific competition goals. Check out the details at this link for all our WOOT programs in math, computer science, chemistry, and physics.

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)!

Be sure to mark your calendars for the following events:
[list][*]April 3rd (Webinar), 4pm PT/7:00pm ET, Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor
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April 9th (Webinar), 4:00pm PT/7:00pm ET, Learn about Video-based Summer Camps at the Virtual Campus
[*]April 10th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MathILy and MathILy-Er Math Jam: Multibackwards Numbers
[*]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
Combinatorics or algebra?
persamaankuadrat   0
7 minutes ago
Source: OSNK 2024
How many sequences of $\left(a_{1},a_{2},a_{3},a_{4},a_{5},a_{6} \right)$ where the $a_{i}$ are positive integers such that each $1 \le a_{i} \le 4$ and none of two consecutive terms when summed are equal to $4$.
0 replies
persamaankuadrat
7 minutes ago
0 replies
Inspired by old results
sqing   4
N 17 minutes ago by sqing
Source: Own
Let $ a,b\geq 0 $ and $  a^2+ab+b^2=2$ . Prove that
$$ (a+b-ab)\left( \frac{1}{a+1} + \frac{1}{b+1}\right)\leq 2 $$$$ (a+b-ab)\left( \frac{a}{b+1} + \frac{2b}{a+2}\right)\leq 2 $$$$ (a+b-ab)\left( \frac{a}{b+1} + \frac{2b}{a+1}\right)\leq 4$$Let $ a,b  $ be reals such that $  a^2+b^2=2$ . Prove that
$$ (a+b)\left( \frac{1}{a+1} + \frac{1}{b+1}\right)= 2 $$$$ (a+b)\left( \frac{a}{b+1} + \frac{b}{a+1}\right)=2 $$
4 replies
1 viewing
sqing
4 hours ago
sqing
17 minutes ago
Hard limits
Snoop76   5
N 29 minutes ago by Snoop76
$a_n$ and $b_n$ satisfies the following recursion formulas: $a_{0}=1, $ $b_{0}=1$, $ a_{n+1}=a_{n}+b_{n}$$ $ and $ $$ b_{n+1}=(2n+3)b_{n}+a_{n}$. Find $ \lim_{n \to \infty} \frac{a_n}{(2n-1)!!}$ $ $ and $ $ $\lim_{n \to \infty} \frac{b_n}{(2n+1)!!}.$
5 replies
1 viewing
Snoop76
Mar 25, 2025
Snoop76
29 minutes ago
This problem has unintended solution, found by almost all who solved it :(
mshtand1   6
N 32 minutes ago by ayeen_izady
Source: Ukrainian Mathematical Olympiad 2025. Day 2, Problem 11.7
Given a triangle \(ABC\), an arbitrary point \(D\) is chosen on the side \(AC\). In triangles \(ABD\) and \(CBD\), the angle bisectors \(BK\) and \(BL\) are drawn, respectively. The point \(O\) is the circumcenter of \(\triangle KBL\). Prove that the second intersection point of the circumcircles of triangles \(ABL\) and \(CBK\) lies on the line \(OD\).

Proposed by Anton Trygub
6 replies
mshtand1
Mar 14, 2025
ayeen_izady
32 minutes ago
Number Theory Chain!
JetFire008   45
N 35 minutes ago by Seungjun_Lee
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
45 replies
JetFire008
Apr 7, 2025
Seungjun_Lee
35 minutes ago
Easy algebra
Namisgood   2
N 35 minutes ago by Namisgood
Source: Indian mathematics olympiad Stage-I 2014(PRMO)
For a natural number b, let N(b) denote the number of natural numbers for which the equation x^2+ax+b has integer roots. What is the smallest value of b for which N(b)=20
2 replies
Namisgood
Mar 31, 2025
Namisgood
35 minutes ago
Why can't we just write down an FE?
TheUltimate123   5
N 41 minutes ago by jasperE3
Source: CAMO 2022/2 (https://aops.com/community/c594864h2791269p24548889)
Find all functions \(f:\mathbb Z\to\mathbb Z\) such that \[f(f(x)f(y))=f(xf(y))+f(y)\]for all integers \(x\) and \(y\).

Proposed by nukelauncher and TheUltimate123
5 replies
TheUltimate123
Mar 20, 2022
jasperE3
41 minutes ago
Very tight inequalities
KhuongTrang   3
N an hour ago by KhuongTrang
Source: own
Problem. Given non-negative real numbers $a,b,c$ satisfying $ab+bc+ca=1.$ Prove that $$\color{black}{\frac{1}{35a+12b+2}+\frac{1}{35b+12c+2}+\frac{1}{35c+12a+2}\ge \frac{4}{39}.}$$$$\color{black}{\frac{1}{4a+9b+6}+\frac{1}{4b+9c+6}+\frac{1}{4c+9a+6}\le \frac{2}{9}.}$$When does equality hold?
3 replies
KhuongTrang
May 17, 2024
KhuongTrang
an hour ago
Prove that d >= p-1
tranthanhnam   14
N 2 hours ago by Ilikeminecraft
Source: IMO Shortlist 1997, Q12
Let $ p$ be a prime number and $ f$ an integer polynomial of degree $ d$ such that $ f(0) = 0,f(1) = 1$ and $ f(n)$ is congruent to $ 0$ or $ 1$ modulo $ p$ for every integer $ n$. Prove that $ d\geq p - 1$.
14 replies
tranthanhnam
Aug 26, 2005
Ilikeminecraft
2 hours ago
Quick NT
AndreiVila   3
N 2 hours ago by Rohit-2006
Source: Mathematical Minds 2024 P1
Find all positive integers $n\geqslant 2$ such that $d_{i+1}/d_i$ is an integer for all $1\leqslant i < k$, where $1=d_1<d_2<\dots <d_k=n$ are all the positive divisors of $n$.

Proposed by Pavel Ciurea
3 replies
AndreiVila
Sep 29, 2024
Rohit-2006
2 hours ago
Problem 3 IMO 2005 (Day 1)
Valentin Vornicu   120
N 2 hours ago by Nguyenhuyen_AG
Let $x,y,z$ be three positive reals such that $xyz\geq 1$. Prove that
\[ \frac { x^5-x^2 }{x^5+y^2+z^2} + \frac {y^5-y^2}{x^2+y^5+z^2} + \frac {z^5-z^2}{x^2+y^2+z^5} \geq 0 . \]
Hojoo Lee, Korea
120 replies
Valentin Vornicu
Jul 13, 2005
Nguyenhuyen_AG
2 hours ago
Transform the sequence
steven_zhang123   0
3 hours ago
Given a sequence of \( n \) real numbers \( a_1, a_2, \ldots, a_n \), we can select a real number \( \alpha \) and transform the sequence into \( |a_1 - \alpha|, |a_2 - \alpha|, \ldots, |a_n - \alpha| \). This transformation can be performed multiple times, with each chosen real number \( \alpha \) potentially being different
(i) Prove that it is possible to transform the sequence into all zeros after a finite number of such transformations.
(ii) To ensure that the above result can be achieved for any given initial sequence, what is the minimum number of transformations required?
0 replies
steven_zhang123
3 hours ago
0 replies
prove that any quadrilateral satisfying this inequality is a trapezoid
mqoi_KOLA   3
N 3 hours ago by mqoi_KOLA
Prove that any Trapezoid/trapzium satisfies the given inequality$$
|r - p| < q + s < r + p
$$where $p,r$ are lengths of parallel sides and $q,s$ are other two sides.
3 replies
mqoi_KOLA
Yesterday at 3:48 AM
mqoi_KOLA
3 hours ago
Find the angle
Alfombraking   0
3 hours ago
Inside a right triangle ABC at , point Q is located, which belongs to the bisector of angle C. On the extension of BQ, point P is located from which PM⊥CQ(M en CQ) is drawn, such that BP=2(MC). If AQ=BC, then the measure of angle BAQ is.
0 replies
Alfombraking
3 hours ago
0 replies
Geometry problem-second time posting
kjhgyuio   0
Apr 4, 2025
Source: smo roudn 2

A square is cut into several rectangles, none of which is a square ,so that the sides of each rectangles are parallel to the sides of a square .For each rectangle with sides a,b,a<b compute the ratio a/b Prove that the sum of these ratios is at least 1
0 replies
kjhgyuio
Apr 4, 2025
0 replies
Geometry problem-second time posting
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Source: smo roudn 2
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kjhgyuio
34 posts
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A square is cut into several rectangles, none of which is a square ,so that the sides of each rectangles are parallel to the sides of a square .For each rectangle with sides a,b,a<b compute the ratio a/b Prove that the sum of these ratios is at least 1
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