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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
easy number theory sequnce problem
skellyrah   0
3 minutes ago
Source: simillar to 2016 Greece,Team Selection Test,Problem
Define the sequnce ${(a_n)}_{n\ge0}$ by $a_0=3$ and $a_n=2a_{n-1}-3$
Determine all positive integers $m$ such that $\gcd (m,a_n)=1 \ , \ \forall n\geq 0$.
0 replies
skellyrah
3 minutes ago
0 replies
Random concyclicity in a square config
Maths_VC   6
N 10 minutes ago by Assassino9931
Source: Serbia JBMO TST 2025, Problem 1
Let $M$ be a random point on the smaller arc $AB$ of the circumcircle of square $ABCD$, and let $N$ be the intersection point of segments $AC$ and $DM$. The feet of the tangents from point $D$ to the circumcircle of the triangle $OMN$ are $P$ and $Q$ , where $O$ is the center of the square. Prove that points $A$, $C$, $P$ and $Q$ lie on a single circle.
6 replies
Maths_VC
May 27, 2025
Assassino9931
10 minutes ago
Maxi-inequality
giangtruong13   1
N 18 minutes ago by giangtruong13
Let $a,b,c >0$ and $a+b+c=2abc$. Find max: $$P= \sum_{cyc} \frac{a+2}{\sqrt{6(a^2+2)}}$$
1 reply
giangtruong13
Yesterday at 3:42 PM
giangtruong13
18 minutes ago
Product of opposite sides
nabodorbuco2   1
N 20 minutes ago by Beelzebub
Source: Original
Let $ABCDEF$ a regular hexagon inscribed in a circle $\Omega$. Let $P_i$ be a point inside $\Omega$ and $P_e$ its polar reflection wrt $\Omega$. The rays $AP_i,BP_i,CP_i,DP_i,EP_i,FP_i$ meet $\Omega$ again at $A_i,B_i,C_i,D_i,E_i,F_i$. Call $Q_I$ the polygon formed by the vertices $A_i,B_i,C_i,D_i,E_i,F_i$. Similarly construct the polygon $Q_E$ using $P_e$ instead.

Show that $Q_I$ and $Q_E$ are congruent.
1 reply
nabodorbuco2
2 hours ago
Beelzebub
20 minutes ago
Circle is tangent to circumcircle and incircle
ABCDE   75
N 23 minutes ago by ohiorizzler1434
Source: 2016 ELMO Problem 6
Elmo is now learning olympiad geometry. In triangle $ABC$ with $AB\neq AC$, let its incircle be tangent to sides $BC$, $CA$, and $AB$ at $D$, $E$, and $F$, respectively. The internal angle bisector of $\angle BAC$ intersects lines $DE$ and $DF$ at $X$ and $Y$, respectively. Let $S$ and $T$ be distinct points on side $BC$ such that $\angle XSY=\angle XTY=90^\circ$. Finally, let $\gamma$ be the circumcircle of $\triangle AST$.

(a) Help Elmo show that $\gamma$ is tangent to the circumcircle of $\triangle ABC$.

(b) Help Elmo show that $\gamma$ is tangent to the incircle of $\triangle ABC$.

James Lin
75 replies
ABCDE
Jun 24, 2016
ohiorizzler1434
23 minutes ago
Number of divisors divides n^2 + 1
dolphinday   3
N an hour ago by sansgankrsngupta
Source: Krishna Pothapragada
Let $n$ be an even integer, and let $d(n)$ denote the number of (positive) divisors of $n$.
Prove that $d(n)$ does not divide $n^2+1$.

Written by Krishna Pothapragada
3 replies
+1 w
dolphinday
Jan 10, 2024
sansgankrsngupta
an hour ago
Own made functional equation
Primeniyazidayi   5
N an hour ago by JARP091
Source: own(probably)
Find all functions $f:R \rightarrow R$ such that $xf(x^2+2f(y)-yf(x))=f(x)^3-f(y)(f(x^2)-2f(x))$ for all $x,y \in \mathbb{R}$
5 replies
Primeniyazidayi
May 26, 2025
JARP091
an hour ago
Iran TST P6
luutrongphuc   4
N 2 hours ago by AblonJ
Find all function $f: \mathbb{R^+} \to \mathbb{R^+}$ such that:
$$f \left( f(f(xy))+x^2\right)=f(y)f(x)-f(y)f(x+y)$$
4 replies
luutrongphuc
May 26, 2025
AblonJ
2 hours ago
Brilliant Problem
M11100111001Y1R   7
N 2 hours ago by flower417477
Source: Iran TST 2025 Test 3 Problem 3
Find all sequences \( (a_n) \) of natural numbers such that for every pair of natural numbers \( r \) and \( s \), the following inequality holds:
\[
\frac{1}{2} < \frac{\gcd(a_r, a_s)}{\gcd(r, s)} < 2
\]
7 replies
M11100111001Y1R
May 27, 2025
flower417477
2 hours ago
In Cyclic Quadrilateral ABCD, find AB^2+BC^2-CD^2-AD^2
Darealzolt   1
N 2 hours ago by Beelzebub
Source: KTOM April 2025 P8
Given Cyclic Quadrilateral \(ABCD\) with an area of \(2025\), with \(\angle ABC = 45^{\circ}\). If \( 2AC^2 = AB^2+BC^2+CD^2+DA^2\), Hence find the value of \(AB^2+BC^2-CD^2-DA^2\).
1 reply
Darealzolt
Today at 4:10 AM
Beelzebub
2 hours ago
Another FE
M11100111001Y1R   3
N 2 hours ago by AndreiVila
Source: Iran TST 2025 Test 2 Problem 3
Find all functions $f: \mathbb{R}^+ \to \mathbb{R}^+$ such that for all $x,y>0$ we have:
$$f(f(f(xy))+x^2)=f(y)(f(x)-f(x+y))$$
3 replies
1 viewing
M11100111001Y1R
Yesterday at 8:03 AM
AndreiVila
2 hours ago
Iran TST Starter
M11100111001Y1R   4
N 2 hours ago by flower417477
Source: Iran TST 2025 Test 1 Problem 1
Let \( a_n \) be a sequence of positive real numbers such that for every \( n > 2025 \), we have:
\[
a_n = \max_{1 \leq i \leq 2025} a_{n-i} - \min_{1 \leq i \leq 2025} a_{n-i}
\]Prove that there exists a natural number \( M \) such that for all \( n > M \), the following holds:
\[
a_n < \frac{1}{1404}
\]
4 replies
M11100111001Y1R
May 27, 2025
flower417477
2 hours ago
Inequality with abc=1
tenplusten   10
N 3 hours ago by Adywastaken
Source: JBMO 2011 Shortlist A7
$\boxed{\text{A7}}$ Let $a,b,c$ be positive reals such that $abc=1$.Prove the inequality $\sum\frac{2a^2+\frac{1}{a}}{b+\frac{1}{a}+1}\geq 3$
10 replies
tenplusten
May 15, 2016
Adywastaken
3 hours ago
A game of cutting
k.vasilev   11
N 3 hours ago by NicoN9
Source: All-Russian Olympiad 2019 grade 10 problem 2
Pasha and Vova play the following game, making moves in turn; Pasha moves first. Initially, they have a large piece of plasticine. By a move, Pasha cuts one of the existing pieces into three(of arbitrary sizes), and Vova merges two existing pieces into one. Pasha wins if at some point there appear to be $100$ pieces of equal weights. Can Vova prevent Pasha's win?
11 replies
k.vasilev
Apr 23, 2019
NicoN9
3 hours ago
tangency points to circumcircle coincide
jasperE3   2
N Jul 20, 2022 by Bigtaitus
Source: Brazil TST 1997 Test 1 P1
Let $ABC$ be a triangle and $L$ its circumscribed circle. The internal bisector of angle $A$ meets $BC$ at point $P$. Let $L_1$ be the circle tangent to $AP,BP$ and $L$. Similarly, let $L_2$ be the circle tangent to $AP,CP$ and $L$. Prove that the tangency points of $L_1$ and $L_2$ with $AP$ coincide.
2 replies
jasperE3
May 11, 2021
Bigtaitus
Jul 20, 2022
tangency points to circumcircle coincide
G H J
G H BBookmark kLocked kLocked NReply
Source: Brazil TST 1997 Test 1 P1
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jasperE3
11390 posts
#1 • 3 Y
Y by Mango247, Mango247, Mango247
Let $ABC$ be a triangle and $L$ its circumscribed circle. The internal bisector of angle $A$ meets $BC$ at point $P$. Let $L_1$ be the circle tangent to $AP,BP$ and $L$. Similarly, let $L_2$ be the circle tangent to $AP,CP$ and $L$. Prove that the tangency points of $L_1$ and $L_2$ with $AP$ coincide.
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kvanta
113 posts
#2
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Let $M$ be the midpoint of arc $BC$. Inversion about $M$ with radius $MB$ fixes $B,C$ and so swaps $BC$ and $L$, so it swaps $A$ and $P$. Since it also sends $AM$ to itself, it fixes $L_1$ and $L_2$, and so they're orthogonal to the circle centred at $M$ with radius $MB$. This means that both circles are tangent to $MA$ at the point at distance $MB$ from $M$, i.e. the incentre $I$.
This post has been edited 2 times. Last edited by kvanta, May 11, 2021, 5:23 PM
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Bigtaitus
75 posts
#3
Y by
Call the circumferences $\omega_1$ and $\omega_2$ respectively. Now deffine $P=\omega_1\cap (ABC)$, $M=\omega_1\cap BC$ and $Q=\omega_2\cap (ABC)$, $N=\omega_2\cap BC$. Also let $W$ be the midpont of minor arc $\overset{\frown}{BC}$. Now, it is well-known that $P-M-N$ and $Q-N-W$, and thus we get that $$\angle WMN = \angle PMB$$, but as $BM$ is tangent to $\omega_1$, this angle is the angle of the chord $PM$ in $\omega_1$. But because of the homothety centered in $P$ that sends $\omega_1$ to $(ABC)$ and $M$ to $W$, we get that this angle is also $\angle PQW$. Thus $$\angle WMN = \angle PQN \implies P,Q,M,N$$are concyclic. Thus $$WL_1^2=WM\cdot WP =WN\cdot WQ = WL_2^2$$, and we're done.
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