Plan ahead for the next school year. Schedule your class today!

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k a July Highlights and 2025 AoPS Online Class Information
jwelsh   0
Jul 1, 2025
We are halfway through summer, so be sure to carve out some time to keep your skills sharp and explore challenging topics at AoPS Online and our AoPS Academies (including the Virtual Campus)!

[list][*]Over 60 summer classes are starting at the Virtual Campus on July 7th - check out the math and language arts options for middle through high school levels.
[*]At AoPS Online, we have accelerated sections where you can complete a course in half the time by meeting twice/week instead of once/week, starting on July 8th:
[list][*]MATHCOUNTS/AMC 8 Basics
[*]MATHCOUNTS/AMC 8 Advanced
[*]AMC Problem Series[/list]
[*]Plus, AoPS Online has a special seminar July 14 - 17 that is outside the standard fare: Paradoxes and Infinity
[*]We are expanding our in-person AoPS Academy locations - are you looking for a strong community of problem solvers, exemplary instruction, and math and language arts options? Look to see if we have a location near you and enroll in summer camps or academic year classes today! New locations include campuses in California, Georgia, New York, Illinois, and Oregon and more coming soon![/list]

MOP (Math Olympiad Summer Program) just ended and the IMO (International Mathematical Olympiad) is right around the corner! This year’s IMO will be held in Australia, July 10th - 20th. Congratulations to all the MOP students for reaching this incredible level and best of luck to all selected to represent their countries at this year’s IMO! Did you know that, in the last 10 years, 59 USA International Math Olympiad team members have medaled and have taken over 360 AoPS Online courses. Take advantage of our Worldwide Online Olympiad Training (WOOT) courses
and train with the best! Please note that early bird pricing ends August 19th!
Are you tired of the heat and thinking about Fall? You can plan your Fall schedule now with classes at either AoPS Online, AoPS Academy Virtual Campus, or one of our AoPS Academies around the US.

Our full course list for upcoming classes is below:
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0 replies
jwelsh
Jul 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
Creative Geometry Problem
giratina3   7
N 3 minutes ago by cheltstudent
Let there be a triangle ABC. Let BX bisect CBA, CY bisect ACB, and XY parallel to BC. If AB = 12, BC = 24, and AC = 18, then what is the perimeter of the triangle AXY?

The hint gives away most of the problem, so make sure you consider the problem for a long time before reading it :thumbup:

(The answer is an integer to you coordinate bashers :play_ball:)

Hint
7 replies
giratina3
Yesterday at 8:10 PM
cheltstudent
3 minutes ago
D1033 : A problem of probability for dominoes 3*1
Dattier   5
N 17 minutes ago by NicoN9
Source: les dattes à Dattier
Let $G$ a grid of 9*9, we choose a little square in $G$ of this grid three times, we can choose three times the same.

What the probability of cover with 3*1 dominoes this grid removed by theses little squares (one, two or three) ?
5 replies
Dattier
May 15, 2025
NicoN9
17 minutes ago
Bernoulli Site Percolation
zqy648   1
N 32 minutes ago by EthanWYX2009
Source: 2025 Feb 谜之竞赛-2
Let \( \mathbb{Z}^2 \) denote the set of all integer lattice points in the plane with Cartesian coordinates. A graph \( G = (\mathbb{Z}^2, E) \) is constructed by connecting two lattice points with an edge if their Euclidean distance is $1{}{}{}$. For a positive integer \( n \), define \( f(n) \) as the number of connected subgraphs \( H = (V(H), E(H)) \) of \( G \) satisfying:
\[
\{(0, 0)\} \subseteq V(H) \subseteq \mathbb{Z}^2, \quad |V(H)| = n, \quad E(H) \subseteq E.
\]Prove that there exists a positive constant \( C \) such that for any positive integer \( n \), \(
f(n) \leq C \cdot 7^n.
\)

Proposed by Hanqing Huang and Huankun Guo
1 reply
zqy648
3 hours ago
EthanWYX2009
32 minutes ago
An inequality
TNKT   2
N 34 minutes ago by arqady
Source: Tran Ngoc Khuong Trang
Problem. Let $a,b,c$ be positive real numbers. Prove that $$\sqrt{\frac{(a+b)(a^3+b^3)}{(2a^2+bc)(2b^2+ca)}}+\sqrt{\frac{(b+c)(b^3+c^3)}{(2b^2+ca)(2c^2+ab)}}+\sqrt{\frac{(c+a)(c^3+a^3)}{(2c^2+ab)(2a^2+bc)}}\ge 2.$$
2 replies
TNKT
Jun 15, 2025
arqady
34 minutes ago
The Ratio of Least Common Multiples
Henry_2001   7
N 34 minutes ago by dacashew
Source: CWMI 2018 Q7
Let $p$ and $c$ be an prime and a composite, respectively. Prove that there exist two integers $m,n,$ such that
$$0<m-n<\frac{\textup{lcm}(n+1,n+2,\cdots,m)}{\textup{lcm}(n,n+1,\cdots,m-1)}=p^c.$$
7 replies
Henry_2001
Aug 16, 2018
dacashew
34 minutes ago
problem that i thought of while eating kfc on a train
iwastedmyusername   17
N 36 minutes ago by fruitmonster97
Let $F_n$ be the $n$th Fibonacci number. What is the value of $\sum_{i=1}^{\infty} \frac{F_i}{4^i}=\frac{F_1}{4}+\frac{F_2}{16}+\frac{F_3}{64}+...$?
17 replies
iwastedmyusername
Jul 2, 2025
fruitmonster97
36 minutes ago
Max value of function with f(f(n)) < n+50
Rijul saini   4
N 40 minutes ago by guptaamitu1
Source: India IMOTC Day 3 Problem 2
Let $S$ be the set of all non-decreasing functions $f: \mathbb{N} \rightarrow \mathbb{N}$ satisfying $f(f(n))<n+50$ for all positive integers $n$. Find the maximum value of
$$f(1)+f(2)+f(3)+\cdots+f(2024)+f(2025)$$over all $f \in S$.

Proposed by Shantanu Nene
4 replies
Rijul saini
Jun 4, 2025
guptaamitu1
40 minutes ago
9 Square roots
A7456321   36
N an hour ago by Not__Infinity
Me personally I only have $\sqrt2=1.414$ memorized but I'm sure there are people out there with more!
update: i recently learned $\sqrt3=1.732$

CLICK ON ME YOU KNOW YOU WANT TO
36 replies
A7456321
May 29, 2025
Not__Infinity
an hour ago
Forgotten coaxiality lemma and more
Vivouaf   1
N 2 hours ago by ohiorizzler1434
Source: self discovered
Let $\omega_1$, $\omega_2$ be two circles. We define for a point $X$ in the plane $\mathbb{P}_{\omega}(X)$ to be the power of $X$ wrt to circle $\omega$.
- Prove that the locus of points $X$ such that $\frac{\mathbb{P}_{\omega_1}(X)}{\mathbb{P}_{\omega_2}(X)} = K$ for some real constant $K$ is a circle coaxial to $\omega_1$ and $\omega_2$, which will be denoted by $S_K$.
- Prove that the center $O_K$ of $S_K$, $O_1$ of $\omega_1$, and $O_2$ of $\omega_2$ are such that $\frac{\overline{O_KO_1}}{\overline{O_KO_2}} = K$
1 reply
Vivouaf
4 hours ago
ohiorizzler1434
2 hours ago
Nice Application of Ky-Fan Inequality
zqy648   0
2 hours ago
Source: 2024 April 谜之竞赛-1
Let \( a_1, a_2, \cdots, a_n \) be real numbers in \( (0, \frac{1}{2}] \). Denote by \( Q_1 \) the root mean square of \( a_1, a_2, \cdots, a_n \), and by \( Q_2 \) the root mean square of \( 1 - a_1, 1 - a_2, \cdots, 1 - a_n \). Prove that
\[
\dfrac{Q_1}{\left(\sum\limits_{i=1}^n \sqrt{a_i}\right)^2} \geq \dfrac{Q_2}{\left(\sum\limits_{i=1}^n \sqrt{1-a_i}\right)^2}
\]Proposed by Yuan Zhang
0 replies
zqy648
2 hours ago
0 replies
One of my Favorite Geometry
zqy648   0
2 hours ago
Source: 2024 April 谜之竞赛-2
Let \(ABCD\) be a bicentric quadrilateral with incircle \(\omega\) and circumcircle \(\Omega\). Circle \(c_1\) is tangent to \(\Omega\) at point \(A\) and externally tangent to \(\omega\), while circle \(c_2\) is tangent to \(\Omega\) at point \(C\) and internally tangent to \(\omega\). Prove that one of the intersection points of \(c_1\) and \(c_2\) lies on the diagonal \(AC\).

Proposed by Lolochen(Xiuyi Chen), Shanghai High School
IMAGE
0 replies
zqy648
2 hours ago
0 replies
short geo problem
SYBARUPEMULA   0
2 hours ago
On a right-angled trapezoid $ABCD$, $\angle B = \angle C = 90^o$ and $BC = \sqrt{AB \times CD}$. Prove that
$$\tan \angle DAC = \tan^3 \angle DBC.$$
0 replies
SYBARUPEMULA
2 hours ago
0 replies
Elegant DFT Practice
zqy648   0
2 hours ago
Source: 2024 November 谜之竞赛-3
Given an odd prime \( p \), a permutation \( a_1, a_2, \ldots, a_{p-1} \) of \( 1, 2, \ldots, p-1 \) is called good if for any positive integer \( t \in \{1, 2, \ldots, p-2\} \) and any distinct integers \( i, j \in \{1, 2, \ldots, p-1\} \),
\[a_{i+t} - a_i \not\equiv a_{j+t} - a_j \pmod{p},\]where the subscripts are interpreted modulo \( p-1 \). Determine the number of good permutations.

Proposed by Hengye Zhang
0 replies
zqy648
2 hours ago
0 replies
Grandi Series is weird??
sadas123   7
N Today at 6:16 AM by Not__Infinity
I was just watching this video and I kinda understood what they were saying they said:

$1-1+1-1+1-1+1-1 .... = \frac{1}{2}$

so at first I thought that = 0

but then I realized that if you give an variable such that:

$x= 1-1+1-1+1-1 .....$
then you get
$x = 1-x$
isolating x you get that
$2x = 1$
so
$x= \frac{1}{2}$

is there a way to get the definite answer because I am still confused.
7 replies
sadas123
Today at 12:52 AM
Not__Infinity
Today at 6:16 AM
Personal Modulo Problem (Title: Encrypted Code)
PikaVee   2
N Jun 5, 2025 by Yihangzh
3 Pokemon each have they own number to use on a part of a lock. Star the Pikachu has the number 87, Luna the Eevee has the number 92, and Aero the Mew has the number 79. A part of their code is found in the expression $C \equiv (3S+5L-2A) \bmod 101$.

To double check if it is right then it needs to follow $C \equiv 5 \bmod 8$ and $C \equiv 3 \bmod 11$. If it does follow it then you need to find the sum of the coefficients with the code the code itself, but if not replace the sum of the coefficients with the lowest possible sum of coefficients where $X+Y+Z+C$ in $(XZ+YL-ZA) \bmod 101$ where X, Y, and Z are positive integers more than 0.

Solution
2 replies
PikaVee
Jun 4, 2025
Yihangzh
Jun 5, 2025
Personal Modulo Problem (Title: Encrypted Code)
G H J
G H BBookmark kLocked kLocked NReply
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PikaVee
22 posts
#1
Y by
3 Pokemon each have they own number to use on a part of a lock. Star the Pikachu has the number 87, Luna the Eevee has the number 92, and Aero the Mew has the number 79. A part of their code is found in the expression $C \equiv (3S+5L-2A) \bmod 101$.

To double check if it is right then it needs to follow $C \equiv 5 \bmod 8$ and $C \equiv 3 \bmod 11$. If it does follow it then you need to find the sum of the coefficients with the code the code itself, but if not replace the sum of the coefficients with the lowest possible sum of coefficients where $X+Y+Z+C$ in $(XZ+YL-ZA) \bmod 101$ where X, Y, and Z are positive integers more than 0.

Solution
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Yihangzh
1537 posts
#2
Y by
Solution
Z K Y
The post below has been deleted. Click to close.
This post has been deleted. Click here to see post.
Yihangzh
1537 posts
#3
Y by
Yihangzh wrote:
Solution

oof, I'm so dumb, just realized my mistake
Z K Y
N Quick Reply
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