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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
Yesterday at 11:16 PM
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
Yesterday at 11:16 PM
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
powers of 2
ErTeeEs06   3
N 12 minutes ago by GeorgeMetrical123
Source: BxMO 2025 P4
Let $a_0, a_1, \ldots, a_{10}$ be integers such that, for each $i \in \{0,1,\ldots,2047\}$, there exists a subset $S \subseteq \{0,1,\ldots,10\}$ with
\[
\sum_{j \in S} a_j \equiv i \pmod{2048}.
\]Show that for each $i \in \{0,1,\ldots,10\}$, there is exactly one $j \in \{0,1,\ldots,10\}$ such that $a_j$ is divisible by $2^i$ but not by $2^{i+1}$.

Note: $\sum_{j \in S} a_j$ is the summation notation, for instance, $\sum_{j \in \{2,5\}} a_j = a_2 + a_5$, while for the empty set $\varnothing$, one defines $\sum_{j \in \varnothing} a_j = 0$.
3 replies
ErTeeEs06
Apr 26, 2025
GeorgeMetrical123
12 minutes ago
IMO 2023 P2
799786   92
N 13 minutes ago by L13832
Source: IMO 2023 P2
Let $ABC$ be an acute-angled triangle with $AB < AC$. Let $\Omega$ be the circumcircle of $ABC$. Let $S$ be the midpoint of the arc $CB$ of $\Omega$ containing $A$. The perpendicular from $A$ to $BC$ meets $BS$ at $D$ and meets $\Omega$ again at $E \neq A$. The line through $D$ parallel to $BC$ meets line $BE$ at $L$. Denote the circumcircle of triangle $BDL$ by $\omega$. Let $\omega$ meet $\Omega$ again at $P \neq B$. Prove that the line tangent to $\omega$ at $P$ meets line $BS$ on the internal angle bisector of $\angle BAC$.
92 replies
799786
Jul 8, 2023
L13832
13 minutes ago
Hard inequality
ys33   2
N 28 minutes ago by sqing
Let $a, b, c, d>0$. Prove that
$\sqrt[3]{ab}+ \sqrt[3]{cd} < \sqrt[3]{(a+b+c)(b+c+d)}$.
2 replies
2 viewing
ys33
2 hours ago
sqing
28 minutes ago
Problem 1 (First Day)
Valentin Vornicu   136
N 38 minutes ago by Rayvhs
1. Let $ABC$ be an acute-angled triangle with $AB\neq AC$. The circle with diameter $BC$ intersects the sides $AB$ and $AC$ at $M$ and $N$ respectively. Denote by $O$ the midpoint of the side $BC$. The bisectors of the angles $\angle BAC$ and $\angle MON$ intersect at $R$. Prove that the circumcircles of the triangles $BMR$ and $CNR$ have a common point lying on the side $BC$.
136 replies
Valentin Vornicu
Jul 12, 2004
Rayvhs
38 minutes ago
Hojoo Lee problem 73
Leon   23
N an hour ago by sqing
Source: Belarus 1998
Let $a$, $b$, $c$ be real positive numbers. Show that \[\frac{a}{b}+\frac{b}{c}+\frac{c}{a}\geq \frac{a+b}{b+c}+\frac{b+c}{a+b}+1\]
23 replies
Leon
Aug 21, 2006
sqing
an hour ago
Avoid losing the game
PieAreSquared   17
N an hour ago by Mathgloggers
Source: EGMO 2023/4
Turbo the snail sits on a point on a circle with circumference $1$. Given an infinite sequence of positive real numbers $c_1, c_2, c_3, \dots$, Turbo successively crawls distances $c_1, c_2, c_3, \dots$ around the circle, each time choosing to crawl either clockwise or counterclockwise.
Determine the largest constant $C > 0$ with the following property: for every sequence of positive real numbers $c_1, c_2, c_3, \dots$ with $c_i < C$ for all $i$, Turbo can (after studying the sequence) ensure that there is some point on the circle that it will never visit or crawl across.
17 replies
PieAreSquared
Apr 16, 2023
Mathgloggers
an hour ago
Special line through antipodal
Phorphyrion   10
N an hour ago by SimogmH1
Source: 2025 Israel TST Test 1 P2
Triangle $\triangle ABC$ is inscribed in circle $\Omega$. Let $I$ denote its incenter and $I_A$ its $A$-excenter. Let $N$ denote the midpoint of arc $BAC$. Line $NI_A$ meets $\Omega$ a second time at $T$. The perpendicular to $AI$ at $I$ meets sides $AC$ and $AB$ at $E$ and $F$ respectively. The circumcircle of $\triangle BFT$ meets $BI_A$ a second time at $P$, and the circumcircle of $\triangle CET$ meets $CI_A$ a second time at $Q$. Prove that $PQ$ passes through the antipodal to $A$ on $\Omega$.
10 replies
1 viewing
Phorphyrion
Oct 28, 2024
SimogmH1
an hour ago
Hard trigonometric inequality 2+Σ[cyc](B+C-A)/sinA>(pi/2)Σ[cyc]sinA/sinBsinC
tom-nowy   2
N an hour ago by tom-nowy
Source: https://web.archive.org/web/20220629144937/https://oshiete.goo.ne.jp/qa/13012170.html
For $\bigtriangleup ABC$, prove that
\[ 
2+ \frac{B+C-A}{\sin A} +\frac{C+A-B}{\sin B} +\frac{A+B-C}{\sin C}
 > \frac{\pi}{2}\left( \frac{\sin^2 A+\sin^2 B+\sin^2 C}{\sin A \sin B \sin C } \right) 
\]
2 replies
tom-nowy
Jun 14, 2022
tom-nowy
an hour ago
4 variables with quadrilateral sides
mihaig   6
N an hour ago by mihaig
Source: VL
Let $a,b,c,d\geq0$ satisfying
$$\frac1{a+1}+\frac1{b+1}+\frac1{c+1}+\frac1{d+1}=2.$$Prove
$$4\left(abc+abd+acd+bcd\right)\geq3\left(a+b+c+d\right)+4.$$
6 replies
mihaig
Apr 25, 2025
mihaig
an hour ago
Bigger Cyclic Sets Exist?
FireBreathers   1
N an hour ago by NO_SQUARES
Define the set of numbers $a_1, . . . , a_m$ is $bigger$ than the set of numbers $b_1, . . . , b_n$ if among all inequalities of the form $a_i > b_j$ the number of true inequalities is at least $2$ times greater than the number of false ones. Prove that there do not exist three sets $X, Y, Z$ such that $X$ is $bigger$ than $Y$, $Y$ is $bigger$ than $Z$, $Z$ is $bigger$ than $X$.
1 reply
FireBreathers
an hour ago
NO_SQUARES
an hour ago
Almost Squarefree Integers
oVlad   2
N an hour ago by HeshTarg
Source: Romania Junior TST 2025 Day 1 P1
A positive integer $n\geqslant 3$ is almost squarefree if there exists a prime number $p\equiv 1\bmod 3$ such that $p^2\mid n$ and $n/p$ is squarefree. Prove that for any almost squarefree positive integer $n$ the ratio $2\sigma(n)/d(n)$ is an integer.
2 replies
oVlad
Apr 12, 2025
HeshTarg
an hour ago
D1024 : Can you do that?
Dattier   3
N an hour ago by Dattier
Source: les dattes à Dattier
Let $x_{n+1}=x_n^2+1$ and $x_0=1$.

Can you calculate $\sum\limits_{i=1}^{2^{2025}} x_i \mod 10^{30}$?
3 replies
Dattier
Apr 29, 2025
Dattier
an hour ago
< KCE = < LCP , 4 circles related, hard version
parmenides51   4
N an hour ago by Sivege
Source: 2019 RMM Shortlist G4, version 2 , generalized
Let $\Omega$ be the circumcircle of an acute-angled triangle $ABC$. A point $D$ is chosen on the internal bisector of $\angle ACB$ so that the points $D$ and $C$ are separated by $AB$. A circle $\omega$ centered at $D$ is tangent to the segment $AB$ at $E$. The tangents to $\omega$ through $C$ meet the segment $AB$ at $K$ and $L$, where $K$ lies on the segment $AL$. A circle $\Omega_1$ is tangent to the segments $AL, CL$, and also to $\Omega$ at point $M$. Similarly, a circle $\Omega_2$ is tangent to the segments $BK, CK$, and also to $\Omega$ at point $N$. The lines $LM$ and $KN$ meet at $P$. Prove that $\angle KCE = \angle LCP$.

Poland
4 replies
parmenides51
Jun 18, 2020
Sivege
an hour ago
Find (a,n)
shobber   71
N an hour ago by MATHS_ENTUSIAST
Source: China TST 2006 (1)
Find all positive integer pairs $(a,n)$ such that $\frac{(a+1)^n-a^n}{n}$ is an integer.
71 replies
shobber
Mar 24, 2006
MATHS_ENTUSIAST
an hour ago
computational starting with isosceles triangle
parmenides51   1
N May 27, 2023 by vanstraelen
Source: COFFEE: Carolina González p1 , 9-11 May 2020
Let $ABC$ be an isosceles triangle with $AB = AC$ and $BC = 12$. Let $D$ be the midpoint of $BC$ and let $E$ be a point in $AC$ such that $DE$ is perpendicular to $AC$. The line parallel to $BC$ passing through $E$ intersects side $AB$ at point $F$.If $EC = 4$, determine the length of the segment $EF$.
1 reply
parmenides51
Dec 5, 2021
vanstraelen
May 27, 2023
computational starting with isosceles triangle
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G H BBookmark kLocked kLocked NReply
Source: COFFEE: Carolina González p1 , 9-11 May 2020
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parmenides51
30650 posts
#1
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Let $ABC$ be an isosceles triangle with $AB = AC$ and $BC = 12$. Let $D$ be the midpoint of $BC$ and let $E$ be a point in $AC$ such that $DE$ is perpendicular to $AC$. The line parallel to $BC$ passing through $E$ intersects side $AB$ at point $F$.If $EC = 4$, determine the length of the segment $EF$.
This post has been edited 2 times. Last edited by parmenides51, Dec 5, 2021, 7:28 AM
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vanstraelen
9004 posts
#2
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Given $\triangle ABC\ :\ A(0,a),B(-6,0),C(6,0)$.

Points $D(0,0)$ and $E(\frac{6a^{2}}{a^{2}+36},\frac{36a}{a^{2}+36})$.
$EC=4 \Rightarrow a=3\sqrt{5}$.
Then $EF=\frac{20}{3}$.
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