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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
Interesting integral
tom-nowy   1
N an hour ago by ddot1
Determine the value of \[ \int_{-1}^{1} e^x \sin \sqrt{1-x^2}  \, \mathrm dx .\]
1 reply
tom-nowy
4 hours ago
ddot1
an hour ago
2025 OMOUS Problem 6
enter16180   3
N 2 hours ago by Doru2718
Source: Open Mathematical Olympiad for University Students (OMOUS-2025)
Let $A=\left(a_{i j}\right)_{i, j=1}^{n} \in M_{n}(\mathbb{R})$ be a positive semi-definite matrix. Prove that the matrix $B=\left(b_{i j}\right)_{i, j=1}^{n} \text {, where }$ $b_{i j}=\arcsin \left(x^{i+j}\right) \cdot a_{i j}$, is also positive semi-definite for all $x \in(0,1)$.
3 replies
enter16180
Apr 18, 2025
Doru2718
2 hours ago
Geometry Handout is finally done!
SimplisticFormulas   2
N 4 hours ago by parmenides51
If there’s any typo or problem you think will be a nice addition, do send here!
handout, geometry
2 replies
SimplisticFormulas
Yesterday at 4:58 PM
parmenides51
4 hours ago
Perpendicularity with Incircle Chord
tastymath75025   31
N 5 hours ago by cj13609517288
Source: 2019 ELMO Shortlist G3
Let $\triangle ABC$ be an acute triangle with incenter $I$ and circumcenter $O$. The incircle touches sides $BC,CA,$ and $AB$ at $D,E,$ and $F$ respectively, and $A'$ is the reflection of $A$ over $O$. The circumcircles of $ABC$ and $A'EF$ meet at $G$, and the circumcircles of $AMG$ and $A'EF$ meet at a point $H\neq G$, where $M$ is the midpoint of $EF$. Prove that if $GH$ and $EF$ meet at $T$, then $DT\perp EF$.

Proposed by Ankit Bisain
31 replies
tastymath75025
Jun 27, 2019
cj13609517288
5 hours ago
tangential trapezoid with 2 right angles
parmenides51   1
N Yesterday at 6:44 PM by vanstraelen
Source: 2002 Germany R4 11.6 https://artofproblemsolving.com/community/c3208025_
A trapezoid $ABCD$ with right angles at $A$ and $D$ has an inscribed circle with center $M$ and radius $r$. Let the lengths of the parallel sides $\overline{AB}$ and $\overline{CD}$ be $a$ and $c$, and the intersection of the diagonals $\overline{AC}$ and $\overline{BD}$ be $S$.
1. Prove that the perpendicular from $S$ to one of the trapezoid sides has the length $r$.
2. Determine the distance between $M$ and $S$ as a function of $r$ and $a$.
1 reply
parmenides51
Sep 25, 2024
vanstraelen
Yesterday at 6:44 PM
Neuberg Cubic leads to fixed point
YaoAOPS   1
N Yesterday at 6:02 PM by huoxy1623
Source: own
Let $P$ be a point on the Neuberg cubic. Show that as $P$ varies, the Nine Point Circle of the antipedal triangle of $P$ goes through a fixed point.
1 reply
YaoAOPS
Yesterday at 5:06 PM
huoxy1623
Yesterday at 6:02 PM
D1020 : Special functional equation
Dattier   0
Yesterday at 5:44 PM
Source: les dattes à Dattier
1) Are there any $(f,g) \in C(\mathbb R,\mathbb R_+)$ increasing with
$$\forall x \in \mathbb R, f(x)(\cos(x)+3/2)+g(x)(\sin(x)+3/2)=\exp(x)$$?

2) Are there any $(f,g) \in C(\mathbb R,\mathbb R_+)$ increasing with
$$\forall x \in \mathbb R, f(x)(\cos(x)+3/2)+g(x)(\sin(x)+3/2)=\exp(x/2)$$?
0 replies
Dattier
Yesterday at 5:44 PM
0 replies
Putnam 2005 B1
Kent Merryfield   10
N Yesterday at 5:14 PM by AshAuktober
Find a nonzero polynomial $P(x,y)$ such that $P(\lfloor a\rfloor,\lfloor 2a\rfloor)=0$ for all real numbers $a.$

(Note: $\lfloor v\rfloor$ is the greatest integer less than or equal to $v.$)
10 replies
Kent Merryfield
Dec 5, 2005
AshAuktober
Yesterday at 5:14 PM
lots of perpendicular
m4thbl3nd3r   0
Yesterday at 4:44 PM
Let $\omega$ be the circumcircle of a non-isosceles triangle $ABC$ and $SA$ be a tangent line to $\omega$ ($S\in BC$). Let $AD\perp BC,I$ be midpoint of $BC$ and $IQ\perp AB,AH\perp SO,AH\cap QD=K$. Prove that $SO\parallel CK$
0 replies
m4thbl3nd3r
Yesterday at 4:44 PM
0 replies
Solve All 6 IMO 2024 Problems (42/42), New Framework Looking for Feedback
Blackhole.LightKing   3
N Yesterday at 3:07 PM by DottedCaculator
Hi everyone,

I’ve been experimenting with a different way of approaching mathematical problem solving — a framework that emphasizes recursive structures and symbolic alignment rather than conventional step-by-step strategies.

Using this method, I recently attempted all six problems from IMO 2024 and was able to arrive at what I believe are valid full-mark solutions across the board (42/42 total score, by standard grading).

However, I don’t come from a formal competition background, so I’m sure there are gaps in clarity, communication, or even logic that I’m not fully aware of.

If anyone here is willing to take a look and provide feedback, I’d appreciate it — especially regarding:

The correctness and completeness of the proofs

Suggestions on how to make the ideas clearer or more elegant

Whether this approach has any broader potential or known parallels

I'm here to learn more and improve the presentation and thinking behind the work.

You can download the Solution here.

https://agi-origin.com/assets/pdf/AGI-Origin_IMO_2024_Solution.pdf


Thanks in advance,
— BlackholeLight0


3 replies
Blackhole.LightKing
Yesterday at 12:14 PM
DottedCaculator
Yesterday at 3:07 PM
circle geometry showing perpendicularity
Kyj9981   4
N Yesterday at 2:41 PM by cj13609517288
Two circles $\omega_1$ and $\omega_2$ intersect at points $A$ and $B$. A line through $B$ intersects $\omega_1$ and $\omega_2$ at points $C$ and $D$, respectively. Line $AD$ intersects $\omega_1$ at point $E \neq A$, and line $AC$ intersects $\omega_2$ at point $F \neq A$. If $O$ is the circumcenter of $\triangle AEF$, prove that $OB \perp CD$.
4 replies
Kyj9981
Mar 18, 2025
cj13609517288
Yesterday at 2:41 PM
Prove excircle is tangent to circumcircle
sarjinius   8
N Yesterday at 2:30 PM by Lyzstudent
Source: Philippine Mathematical Olympiad 2025 P4
Let $ABC$ be a triangle with incenter $I$, and let $D$ be a point on side $BC$. Points $X$ and $Y$ are chosen on lines $BI$ and $CI$ respectively such that $DXIY$ is a parallelogram. Points $E$ and $F$ are chosen on side $BC$ such that $AX$ and $AY$ are the angle bisectors of angles $\angle BAE$ and $\angle CAF$ respectively. Let $\omega$ be the circle tangent to segment $EF$, the extension of $AE$ past $E$, and the extension of $AF$ past $F$. Prove that $\omega$ is tangent to the circumcircle of triangle $ABC$.
8 replies
sarjinius
Mar 9, 2025
Lyzstudent
Yesterday at 2:30 PM
Excircle Tangency Points Concyclic with A
tastymath75025   35
N Yesterday at 12:04 PM by bin_sherlo
Source: USA Winter TST for IMO 2019, Problem 6, by Ankan Bhattacharya
Let $ABC$ be a triangle with incenter $I$, and let $D$ be a point on line $BC$ satisfying $\angle AID=90^{\circ}$. Let the excircle of triangle $ABC$ opposite the vertex $A$ be tangent to $\overline{BC}$ at $A_1$. Define points $B_1$ on $\overline{CA}$ and $C_1$ on $\overline{AB}$ analogously, using the excircles opposite $B$ and $C$, respectively.

Prove that if quadrilateral $AB_1A_1C_1$ is cyclic, then $\overline{AD}$ is tangent to the circumcircle of $\triangle DB_1C_1$.

Ankan Bhattacharya
35 replies
tastymath75025
Jan 21, 2019
bin_sherlo
Yesterday at 12:04 PM
Domain swept by a parabola
Kunihiko_Chikaya   1
N Yesterday at 11:40 AM by Mathzeus1024
Source: 2015 The University of Tokyo entrance exam for Medicine, BS
For a positive real number $a$, consider the following parabola on the coordinate plane.
$C:\ y=ax^2+\frac{1-4a^2}{4a}$
When $a$ ranges over all positive real numbers, draw the domain of the set swept out by $C$.
1 reply
Kunihiko_Chikaya
Feb 25, 2015
Mathzeus1024
Yesterday at 11:40 AM
Romanian National Olympiad 1997 - Grade 11 - Problem 1
Filipjack   2
N Apr 7, 2025 by scannose
Source: Romanian National Olympiad 1997 - Grade 11 - Problem 1
Let $m \ge 2$ and $n \ge 1$ be integers and $A=(a_{ij})$ a square matrix of order $n$ with integer entries. Prove that for any permutation $\sigma \in S_n$ there is a function $\varepsilon : \{1,2,\ldots,n\} \to \{0,1\}$ such that replacing the entries $a_{\sigma(1)1},$ $a_{\sigma(2)2}, $ $\ldots,$ $a_{\sigma(n)n}$ of $A$ respectively by $$a_{\sigma(1)1}+\varepsilon(1), ~a_{\sigma(2)2}+\varepsilon(2), ~\ldots, ~a_{\sigma(n)n}+\varepsilon(n),$$the determinant of the matrix $A_{\varepsilon}$ thus obtained is not divisible by $m.$
2 replies
Filipjack
Apr 6, 2025
scannose
Apr 7, 2025
Romanian National Olympiad 1997 - Grade 11 - Problem 1
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G H BBookmark kLocked kLocked NReply
Source: Romanian National Olympiad 1997 - Grade 11 - Problem 1
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Filipjack
872 posts
#1
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Let $m \ge 2$ and $n \ge 1$ be integers and $A=(a_{ij})$ a square matrix of order $n$ with integer entries. Prove that for any permutation $\sigma \in S_n$ there is a function $\varepsilon : \{1,2,\ldots,n\} \to \{0,1\}$ such that replacing the entries $a_{\sigma(1)1},$ $a_{\sigma(2)2}, $ $\ldots,$ $a_{\sigma(n)n}$ of $A$ respectively by $$a_{\sigma(1)1}+\varepsilon(1), ~a_{\sigma(2)2}+\varepsilon(2), ~\ldots, ~a_{\sigma(n)n}+\varepsilon(n),$$the determinant of the matrix $A_{\varepsilon}$ thus obtained is not divisible by $m.$
This post has been edited 3 times. Last edited by Filipjack, Apr 6, 2025, 10:58 AM
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paxtonw
28 posts
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Let \( A \) be a square matrix with integer entries modulo \( m \), and fix a permutation \( \sigma \in S_n \). Consider the function \( \varepsilon : \{1, 2, \ldots, n\} \to \{0, 1\} \) chosen uniformly at random. The determinant of the modified matrix is a degree-1 polynomial in each \( \varepsilon(i) \), so over \( \mathbb{F}_m \) it is not identically zero (since it includes a monomial corresponding to the sign of \( \sigma \)), thus there exists a choice of \( \varepsilon \) such that the determinant is nonzero modulo \( m \), i.e., not divisible by \( m \).
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scannose
1004 posts
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is this correct? this is my first post in this forum
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