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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.

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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
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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
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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
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Function Problem
Geometry285   3
N 28 minutes ago by Saucepan_man02
The function $f(x)$ can be defined as a sequence such that $x=n$, and $a_n = | a_{n-1} | + \left \lceil \frac{n!}{n^{100}} \right \rceil$, such that $a_n = n$. The function $g(x)$ is such that $g(x) = x!(x+1)!$. How many numbers within the interval $0<n<101$ for the function $g(f(x))$ are perfect squares?
3 replies
Geometry285
Apr 11, 2021
Saucepan_man02
28 minutes ago
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Vieta's Relations
P162008   7
N 2 hours ago by alexheinis
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
7 replies
P162008
2 hours ago
alexheinis
2 hours ago
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Three numbers cannot be squares simultaneously
WakeUp   38
N 2 hours ago by SomeonecoolLovesMaths
Source: APMO 2011
Let $a,b,c$ be positive integers. Prove that it is impossible to have all of the three numbers $a^2+b+c,b^2+c+a,c^2+a+b$ to be perfect squares.
38 replies
WakeUp
May 18, 2011
SomeonecoolLovesMaths
2 hours ago
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Inequalities
sqing   4
N 2 hours ago by ytChen
Let $ a,b,c\geq 0 ,a+b+c\leq 3. $ Prove that
$$a^2+b^2+c^2+ab +2ca+2bc + abc \leq \frac{251}{27}$$$$ a^2+b^2+c^2+ab+2ca+2bc + \frac{2}{5}abc \leq \frac{4861}{540}$$$$ a^2+b^2+c^2+ab+2ca+2bc + \frac{7}{20}abc \leq \frac{2381411}{26460}$$
4 replies
sqing
Yesterday at 12:47 PM
ytChen
2 hours ago
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Primes and sets
mathisreaI   40
N 3 hours ago by Tinoba-is-emotional
Source: IMO 2022 Problem 3
Let $k$ be a positive integer and let $S$ be a finite set of odd prime numbers. Prove that there is at most one way (up to rotation and reflection) to place the elements of $S$ around the circle such that the product of any two neighbors is of the form $x^2+x+k$ for some positive integer $x$.
40 replies
mathisreaI
Jul 13, 2022
Tinoba-is-emotional
3 hours ago
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BMT Algebra #6 - Sum with Combinations
asbodke   2
N 3 hours ago by P162008
Given that $\tbinom{n}{k}=\tfrac{n!}{k!(n-k)!}$, the value of $$\sum_{n=3}^{10}\frac{\binom{n}{2}}{\binom{n}{3}\binom{n+1}{3}}$$can be written in the form $\tfrac{m}{n}$, where $m$ and $n$ are relatively prime positive integers. Compute $m+n$.
2 replies
asbodke
Oct 11, 2020
P162008
3 hours ago
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Problem G5 - IMO Shortlist 2007
April   30
N 4 hours ago by Double07
Source: ISL 2007, G5, AIMO 2008, TST 3, P2
Let $ ABC$ be a fixed triangle, and let $ A_1$, $ B_1$, $ C_1$ be the midpoints of sides $ BC$, $ CA$, $ AB$, respectively. Let $ P$ be a variable point on the circumcircle. Let lines $ PA_1$, $ PB_1$, $ PC_1$ meet the circumcircle again at $ A'$, $ B'$, $ C'$, respectively. Assume that the points $ A$, $ B$, $ C$, $ A'$, $ B'$, $ C'$ are distinct, and lines $ AA'$, $ BB'$, $ CC'$ form a triangle. Prove that the area of this triangle does not depend on $ P$.

Author: Christopher Bradley, United Kingdom
30 replies
April
Jul 13, 2008
Double07
4 hours ago
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Self-evident inequality trick
Lukaluce   16
N 4 hours ago by ErTeeEs06
Source: 2025 Junior Macedonian Mathematical Olympiad P4
Let $x, y$, and $z$ be positive real numbers, such that $x^2 + y^2 + z^2 = 3$. Prove the inequality
\[\frac{x^3}{2 + x} + \frac{y^3}{2 + y} + \frac{z^3}{2 + z} \ge 1.\]When does the equality hold?
16 replies
Lukaluce
May 18, 2025
ErTeeEs06
4 hours ago
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Help my diagram has too many points
MarkBcc168   29
N 5 hours ago by VideoCake
Source: IMO Shortlist 2023 G6
Let $ABC$ be an acute-angled triangle with circumcircle $\omega$. A circle $\Gamma$ is internally tangent to $\omega$ at $A$ and also tangent to $BC$ at $D$. Let $AB$ and $AC$ intersect $\Gamma$ at $P$ and $Q$ respectively. Let $M$ and $N$ be points on line $BC$ such that $B$ is the midpoint of $DM$ and $C$ is the midpoint of $DN$. Lines $MP$ and $NQ$ meet at $K$ and intersect $\Gamma$ again at $I$ and $J$ respectively. The ray $KA$ meets the circumcircle of triangle $IJK$ again at $X\neq K$.

Prove that $\angle BXP = \angle CXQ$.

Kian Moshiri, United Kingdom
29 replies
MarkBcc168
Jul 17, 2024
VideoCake
5 hours ago
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A problem with series
Pena317   1
N 5 hours ago by venhancefan777
Source: P5, Mexico Center Regional Olympiad 2019
A serie of positive integers $a_{1}$,$a_{2}$,. . . ,$a_{n}$ is $auto-delimited$ if for every index $i$ that holds $1\leq i\leq n$, there exist at least $a_{i}$ terms of the serie such that they are all less or equal to $i$.
Find the maximum value of the sum $a_{1}+a_{2}+\cdot \cdot \cdot+a_{n}$, where $a_{1}$,$a_{2}$,. . . ,$a_{n}$ is an $auto-delimited$ serie.
1 reply
Pena317
Nov 28, 2019
venhancefan777
5 hours ago
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IMO 2009, problem 4
ZetaX   60
N 5 hours ago by FarrukhBurzu
Let $ ABC$ be a triangle with $ AB = AC$ . The angle bisectors of $ \angle C AB$ and $ \angle AB C$ meet the sides $ B C$ and $ C A$ at $ D$ and $ E$ , respectively. Let $ K$ be the incentre of triangle $ ADC$. Suppose that $ \angle B E K = 45^\circ$ . Find all possible values of $ \angle C AB$ .

Jan Vonk, Belgium, Peter Vandendriessche, Belgium and Hojoo Lee, Korea
60 replies
ZetaX
Jul 16, 2009
FarrukhBurzu
5 hours ago
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Tennis tournament with rotating courts
v_Enhance   6
N 5 hours ago by Blast_S1
Source: ELMO Shortlist 2013: Problem C10, by Ray Li
Let $N\ge2$ be a fixed positive integer. There are $2N$ people, numbered $1,2,...,2N$, participating in a tennis tournament. For any two positive integers $i,j$ with $1\le i<j\le 2N$, player $i$ has a higher skill level than player $j$. Prior to the first round, the players are paired arbitrarily and each pair is assigned a unique court among $N$ courts, numbered $1,2,...,N$.

During a round, each player plays against the other person assigned to his court (so that exactly one match takes place per court), and the player with higher skill wins the match (in other words, there are no upsets). Afterwards, for $i=2,3,...,N$, the winner of court $i$ moves to court $i-1$ and the loser of court $i$ stays on court $i$; however, the winner of court 1 stays on court 1 and the loser of court 1 moves to court $N$.

Find all positive integers $M$ such that, regardless of the initial pairing, the players $2, 3, \ldots, N+1$ all change courts immediately after the $M$th round.

Proposed by Ray Li
6 replies
v_Enhance
Jul 23, 2013
Blast_S1
5 hours ago
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∑(a-b)(a-c)/(2a^2 + (b+c)^2) >= 0
Zhero   24
N 6 hours ago by RevolveWithMe101
Source: ELMO Shortlist 2010, A2
Let $a,b,c$ be positive reals. Prove that
\[ \frac{(a-b)(a-c)}{2a^2 + (b+c)^2} + \frac{(b-c)(b-a)}{2b^2 + (c+a)^2} + \frac{(c-a)(c-b)}{2c^2 + (a+b)^2} \geq 0. \]

Calvin Deng.
24 replies
Zhero
Jul 5, 2012
RevolveWithMe101
6 hours ago
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i am not abel to prove or disprove
frost23   8
N 6 hours ago by frost23
Source: made on my own
sorrrrrry
8 replies
frost23
Yesterday at 5:20 PM
frost23
6 hours ago
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Two problems
Vulch   1
N Apr 10, 2025 by Lankou
Solve the following problems:
1 reply
Vulch
Apr 10, 2025
Lankou
Apr 10, 2025
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Two problems
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Reveal topic tags
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Vulch
2700 posts
Vulch
#1 h  Apr 10, 2025, 10:58 AM
Y by
Solve the following problems:
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Lankou
1405 posts
Lankou
#2 h  Apr 10, 2025, 11:47 AM
Y by
27.
Using Vieta you get $c=7\cdot8=56$ and $-b=8-3=5$, $b=-5$

28.
If $\Delta<0$ then $f(x)\neq0$
if $\Delta>0$ then $f(x)=0$ has two real roots, one of them may be $0$
This post has been edited 1 time. Last edited by Lankou, Apr 10, 2025, 11:51 AM
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