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k a June Highlights and 2025 AoPS Online Class Information
jlacosta   0
Today at 3:57 PM
Congratulations to all the mathletes who competed at National MATHCOUNTS! If you missed the exciting Countdown Round, you can watch the video at this link. Are you interested in training for MATHCOUNTS or AMC 10 contests? How would you like to train for these math competitions in half the time? We have accelerated sections which meet twice per week instead of once starting on July 8th (7:30pm ET). These sections fill quickly so enroll today!

[list][*]MATHCOUNTS/AMC 8 Basics
[*]MATHCOUNTS/AMC 8 Advanced
[*]AMC 10 Problem Series[/list]
For those interested in Olympiad level training in math, computer science, physics, and chemistry, be sure to enroll in our WOOT courses before August 19th to take advantage of early bird pricing!

Summer camps are starting this 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 a transformative 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][*]June 5th, Thursday, 7:30pm ET: Open Discussion with Ben Kornell and Andrew Sutherland, Art of Problem Solving's incoming CEO Ben Kornell and CPO Andrew Sutherland host an Ask Me Anything-style chat. Come ask your questions and get to know our incoming CEO & CPO!
[*]June 9th, Monday, 7:30pm ET, Game Jam: Operation Shuffle!, Come join us to play our second round of Operation Shuffle! If you enjoy number sense, logic, and a healthy dose of luck, this is the game for you. No specific math background is required; all are welcome.[/list]
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0 replies
jlacosta
Today at 3:57 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
Similarity of two triangles!
ariopro1387   2
N 19 minutes ago by sami1618
Source: Iran Team selection test 2025 - P5
In a scalene triangle $ABC$, $D$ is the point of tangency of the incircle with the side $BC$. Points $T_B$ and $T_C$ are the intersections of the angle bisectors of $\angle ABC$ and $\angle ACB$ with the circumcircle of $ABC$, respectively. Let $X_B$ be the antipodal point of $A$ in the circumcircle of $ACD$, and let $X_C$ be the antipodal point of $A$ in the circumcircle of $ABD$.
Prove that triangles $B T_C X_C$ and $C T_B X_B$ are similar.
2 replies
ariopro1387
May 27, 2025
sami1618
19 minutes ago
IMO Genre Predictions
ohiorizzler1434   78
N 24 minutes ago by ohiorizzler1434
Everybody, with IMO upcoming, what are you predictions for the problem genres?


Personally I predict: predict
78 replies
1 viewing
ohiorizzler1434
May 3, 2025
ohiorizzler1434
24 minutes ago
The Return of Triangle Geometry
peace09   12
N 32 minutes ago by peace09
Source: 2023 ISL A7
Let $N$ be a positive integer. Prove that there exist three permutations $a_1,\dots,a_N$, $b_1,\dots,b_N$, and $c_1,\dots,c_N$ of $1,\dots,N$ such that \[\left|\sqrt{a_k}+\sqrt{b_k}+\sqrt{c_k}-2\sqrt{N}\right|<2023\]for every $k=1,2,\dots,N$.
12 replies
peace09
Jul 17, 2024
peace09
32 minutes ago
Find Triples of Integers
termas   40
N 37 minutes ago by monval
Source: IMO 2015 problem 2
Find all positive integers $(a,b,c)$ such that
$$ab-c,\quad bc-a,\quad ca-b$$are all powers of $2$.

Proposed by Serbia
40 replies
termas
Jul 10, 2015
monval
37 minutes ago
AT // BC wanted
parmenides51   106
N 44 minutes ago by happypi31415
Source: IMO 2019 SL G1
Let $ABC$ be a triangle. Circle $\Gamma$ passes through $A$, meets segments $AB$ and $AC$ again at points $D$ and $E$ respectively, and intersects segment $BC$ at $F$ and $G$ such that $F$ lies between $B$ and $G$. The tangent to circle $BDF$ at $F$ and the tangent to circle $CEG$ at $G$ meet at point $T$. Suppose that points $A$ and $T$ are distinct. Prove that line $AT$ is parallel to $BC$.

(Nigeria)
106 replies
parmenides51
Sep 22, 2020
happypi31415
44 minutes ago
Divisibility of polynomials
avatarofakato   2
N an hour ago by fe.
Source: Polish MO second round 2011
There are two given different polynomials $P(x),Q(x)$ with real coefficients such that $P(Q(x))=Q(P(x))$. Prove that $\forall n\in \mathbb{Z_{+}}$ polynomial:
\[\underbrace{P(P(\ldots P(P}_{n}(x))\ldots))- \underbrace{Q(Q(\ldots Q(Q}_{n}(x))\ldots))\]
is divisible by $P(x)-Q(x)$.
2 replies
avatarofakato
Feb 19, 2012
fe.
an hour ago
2-var inequality
sqing   16
N 2 hours ago by ytChen
Source: Own
Let $ a,b> 0 ,a^3+ab+b^3=3.$ Prove that
$$ (a+b)(a+1)(b+1) \leq 8$$$$ (a^2+b^2)(a+1)(b+1) \leq 8$$Let $ a,b> 0 ,a^3+ab(a+b)+b^3=3.$ Prove that
$$ (a+b)(a+1)(b+1) \leq \frac{3}{2}+\sqrt[3]{6}+\sqrt[3]{36}$$
16 replies
sqing
May 31, 2025
ytChen
2 hours ago
Another right angled triangle
ariopro1387   6
N 2 hours ago by sami1618
Source: Iran Team selection test 2025 - P7
Let $ABC$ be a right angled triangle with $\angle A=90$.Let $M$ be the midpoint of $BC$, and $P$ be an arbitrary point on $AM$. The reflection of $BP$ over $AB$ intersects lines $AC$ and $AM$ at $T$ and $Q$, respectively. The circumcircles of $BPQ$ and $ABC$ intersect again at $F$. Prove that the center of the circumcircle of $CFT$ lies on $BQ$.
6 replies
ariopro1387
May 25, 2025
sami1618
2 hours ago
IMO Shortlist 2012, Number Theory 5
lyukhson   32
N 2 hours ago by awesomeming327.
Source: IMO Shortlist 2012, Number Theory 5
For a nonnegative integer $n$ define $\operatorname{rad}(n)=1$ if $n=0$ or $n=1$, and $\operatorname{rad}(n)=p_1p_2\cdots p_k$ where $p_1<p_2<\cdots <p_k$ are all prime factors of $n$. Find all polynomials $f(x)$ with nonnegative integer coefficients such that $\operatorname{rad}(f(n))$ divides $\operatorname{rad}(f(n^{\operatorname{rad}(n)}))$ for every nonnegative integer $n$.
32 replies
lyukhson
Jul 29, 2013
awesomeming327.
2 hours ago
Number Theory
TheMathBob   4
N 2 hours ago by fe.
Source: Polish Math Olympiad 2021 2nd round p3 day 1
Positive integers $a,b,z$ satisfy the equation $ab=z^2+1$. Prove that there exist positive integers $x,y$ such that
$$\frac{a}{b}=\frac{x^2+1}{y^2+1}$$
4 replies
TheMathBob
Feb 13, 2021
fe.
2 hours ago
IMO Shortlist 2014 N4
hajimbrak   74
N 2 hours ago by LenaEnjoyer
Let $n > 1$ be a given integer. Prove that infinitely many terms of the sequence $(a_k )_{k\ge 1}$, defined by \[a_k=\left\lfloor\frac{n^k}{k}\right\rfloor,\] are odd. (For a real number $x$, $\lfloor x\rfloor$ denotes the largest integer not exceeding $x$.)

Proposed by Hong Kong
74 replies
hajimbrak
Jul 11, 2015
LenaEnjoyer
2 hours ago
USAMO 2003 Problem 1
MithsApprentice   71
N 3 hours ago by cubres
Prove that for every positive integer $n$ there exists an $n$-digit number divisible by $5^n$ all of whose digits are odd.
71 replies
MithsApprentice
Sep 27, 2005
cubres
3 hours ago
IMO ShortList 2008, Number Theory problem 2
April   40
N 4 hours ago by ezpotd
Source: IMO ShortList 2008, Number Theory problem 2, German TST 2, P2, 2009
Let $ a_1$, $ a_2$, $ \ldots$, $ a_n$ be distinct positive integers, $ n\ge 3$. Prove that there exist distinct indices $ i$ and $ j$ such that $ a_i + a_j$ does not divide any of the numbers $ 3a_1$, $ 3a_2$, $ \ldots$, $ 3a_n$.

Proposed by Mohsen Jamaali, Iran
40 replies
April
Jul 9, 2009
ezpotd
4 hours ago
A weird problem
jayme   2
N 4 hours ago by lolsamo
Dear Mathlinkers,

1. ABC a triangle
2. 0 the circumcircle
3. I the incenter
4. 1 a circle passing througn B and C
5. X, Y the second points of intersection of 1 wrt BI, CI
6. 2 the circumcircle of the triangle XYI
7. M, N the symetrics of B, C wrt XY.

Question : if 2 is tangent to 0 then, 2 is tangent to MN.

Sincerely
Jean-Louis
2 replies
jayme
Today at 6:52 AM
lolsamo
4 hours ago
Hard geometry
BoozyCat   2
N Feb 6, 2018 by BoozyCat
Source: SRMC 2017
Quadrilateral $ABCD$ inscribed in a circle $\omega$. Diagonals $AC$ and $BD$ intersect at a point $O$. On segments $AO$ and $DO$ points $E$ and $F$ are selected respectively. Straight $EF$ crosses $\omega$ in points $E_{1}$ and $F_{1}$. The circumscribed circles of triangles $ADE$ and $BCF$ cross the segment $EF$ in points $E_{2}$ and $F_{2}$ respectively (assume that all points $E$, $E_{1}$, $E_{2}$, $F$, $F_{1}$, $F_{2}$ are different). Prove that $E_{1}E_{2}=F_{1}F_{2}$.
2 replies
BoozyCat
Feb 3, 2018
BoozyCat
Feb 6, 2018
Hard geometry
G H J
G H BBookmark kLocked kLocked NReply
Source: SRMC 2017
The post below has been deleted. Click to close.
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BoozyCat
14 posts
#1 • 2 Y
Y by Adventure10, Mango247
Quadrilateral $ABCD$ inscribed in a circle $\omega$. Diagonals $AC$ and $BD$ intersect at a point $O$. On segments $AO$ and $DO$ points $E$ and $F$ are selected respectively. Straight $EF$ crosses $\omega$ in points $E_{1}$ and $F_{1}$. The circumscribed circles of triangles $ADE$ and $BCF$ cross the segment $EF$ in points $E_{2}$ and $F_{2}$ respectively (assume that all points $E$, $E_{1}$, $E_{2}$, $F$, $F_{1}$, $F_{2}$ are different). Prove that $E_{1}E_{2}=F_{1}F_{2}$.
Z K Y
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bobthesmartypants
4337 posts
#2 • 2 Y
Y by Adventure10, Mango247
solution
Z K Y
The post below has been deleted. Click to close.
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BoozyCat
14 posts
#3 • 1 Y
Y by Adventure10
Does anybody have another way to solve?
Z K Y
N Quick Reply
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