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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
Geometry
MTA_2024   6
N 4 minutes ago by mathafou
Let $ABC$ be a triangle such that $AB=3$,$BC=5$ and $AC=6$.Let $D$ be a point on side $AC$ and $E$ one on side $BC$ so that the line $DE$ is tangent to the incircle of $\triangle ABC$ .
Evaluate the perimeter of triangle $\triangle CDE$.
6 replies
MTA_2024
Yesterday at 6:52 PM
mathafou
4 minutes ago
can you solve this..?
Jackson0423   0
13 minutes ago
Source: Own

Find the number of integer pairs \( (x, y) \) satisfying the equation
\[ 4x^2 - 3y^2 = 1 \]such that \( |x| \leq 2025 \).
0 replies
Jackson0423
13 minutes ago
0 replies
JBMO Shortlist 2019 N7
Steve12345   6
N 14 minutes ago by MR.1
Find all perfect squares $n$ such that if the positive integer $a\ge 15$ is some divisor $n$ then $a+15$ is a prime power.

Proposed by Saudi Arabia
6 replies
Steve12345
Sep 12, 2020
MR.1
14 minutes ago
Either you get a 9th degree polynomial, or just easily find using inequality
Sadigly   1
N 15 minutes ago by Sadigly
Source: Azerbaijan Senior MO 2025 P2
Find all the positive reals $x,y,z$ satisfying the following equations: $$y=\frac6{(2x-1)^2}$$$$z=\frac6{(2y-1)^2}$$$$x=\frac6{(2z-1)^2}$$
1 reply
Sadigly
23 minutes ago
Sadigly
15 minutes ago
Gives typical russian combinatorics vibes
Sadigly   0
16 minutes ago
Source: Azerbaijan Senior MO 2025 P3
You are given a positive integer $n$. $n^2$ amount of people stand on coordinates $(x;y)$ where $x,y\in\{0;1;2;...;n-1\}$. Every person got a water cup and two people are considered to be neighbour if the distance between them is $1$. At the first minute, the person standing on coordinates $\{0;0\}$ got $1$ litres of water, and the other $n^2-1$ people's water cup is empty. Every minute, two neighbouring people are chosen that does not have the same amount of water in their water cups, and they equalize the amount of water in their water cups.

Prove that, no matter what, the person standing on the coordinates $\{x;y\}$ will not have more than $\frac1{x+y+1}$ litres of water.
0 replies
Sadigly
16 minutes ago
0 replies
Another thingy inequality
giangtruong13   2
N 18 minutes ago by Double07
Let $a,b,c >0$ such that: $xyz=1$. Prove that: $$\sum_{cyc} \frac{xz+xy}{1+x^3} \leq \sum_{cyc} \frac{1}{x}$$
2 replies
giangtruong13
an hour ago
Double07
18 minutes ago
greatest volume
hzbrl   1
N 25 minutes ago by hzbrl
Source: purple comet
A large sphere with radius 7 contains three smaller balls each with radius 3 . The three balls are each externally tangent to the other two balls and internally tangent to the large sphere. There are four right circular cones that can be inscribed in the large sphere in such a way that the bases of the cones are tangent to all three balls. Of these four cones, the one with the greatest volume has volume $n \pi$. Find $n$.
1 reply
hzbrl
Today at 9:56 AM
hzbrl
25 minutes ago
Easy induction
Sadigly   0
26 minutes ago
Source: Azerbaijan Senior MO 2025 P1
Alice creates a sequence: For the first $2025$ terms of this sequence, she writes the permutation of $\{1;2;3;...;2025\}$. To define the following terms, she does the following: She takes the last $2025$ terms of the sequence, and takes its median. How many values could this sequence's $3000$'th term could get?

(Note: To find the median of $2025$ numbers, you write them in an increasing order,and take the number in the middle)
0 replies
Sadigly
26 minutes ago
0 replies
Kosovo MO 2010 Problem 5
Com10atorics   18
N 33 minutes ago by justaguy_69
Source: Kosovo MO 2010 Problem 5
Let $x,y$ be positive real numbers such that $x+y=1$. Prove that
$\left(1+\frac {1}{x}\right)\left(1+\frac {1}{y}\right)\geq 9$.
18 replies
Com10atorics
Jun 7, 2021
justaguy_69
33 minutes ago
Inspired by my own results
sqing   0
an hour ago
Source: Own
Let $ a,b,c $ be real numbers such that $  a^2+2b^2+4c^2=1. $ Prove that
$$a+2ab+4ca \geq  -\frac{5}{4}\sqrt{ \frac{5}{2}} $$Let $ a,b,c $ be real numbers such that $  a^2+2b^2+c^2=1. $ Prove that
$$a+2ab+4ca \geq  -\frac{1}{24}\sqrt{2951+145\sqrt{145}} $$Let $ a,b,c $ be real numbers such that $ 10a^2+b^2+c^2=1. $ Prove that
$$a+2ab+4ca \geq  -\frac{1}{80}\sqrt{3599+161\sqrt{161}} $$
0 replies
sqing
an hour ago
0 replies
Hard Inequality
William_Mai   13
N an hour ago by sqing
Given $a, b, c \in \mathbb{R}$ such that $a^2 + b^2 + c^2 = 1$.
Find the minimum value of $P = ab + 2bc + 3ca$.

Source: Pham Le Van
13 replies
William_Mai
May 3, 2025
sqing
an hour ago
four point lie on circle
Kizaruno   0
an hour ago
Let triangle ABC be inscribed in a circle with center O. A line d intersects sides AB and AC at points E and D, respectively. Let M, N, and P be the midpoints of segments BD, CE, and DE, respectively. Let Q be the foot of the perpendicular from O to line DE. Prove that the points M, N, P, and Q lie on a circle.
0 replies
Kizaruno
an hour ago
0 replies
official solution of IGO
ABCD1728   3
N an hour ago by WLOGQED1729
Source: IGO official website
Where can I get the official solution of IGO for 2023 and 2024, there are some inhttps://imogeometry.blogspot.com/p/iranian-geometry-olympiad.html, but where can I find them on the official website, thanks :)
3 replies
ABCD1728
May 4, 2025
WLOGQED1729
an hour ago
Inequalities
sqing   0
2 hours ago
Let $ a,b>0, a^2+ab+b^2 \geq 6  $. Prove that
$$a^4+ab+b^4\geq 10$$Let $ a,b>0, a^2+ab+b^2 \leq \sqrt{10}  $. Prove that
$$a^4+ab+b^4  \leq 10$$Let $ a,b>0,  a^2+ab+b^2 \geq \frac{15}{2}  $. Prove that
$$ a^4-ab+b^4\geq 10$$Let $ a,b>0,  a^2+ab+b^2 \leq \sqrt{10}  $. Prove that
$$-\frac{1}{8}\leq  a^4-ab+b^4\leq 10$$
0 replies
sqing
2 hours ago
0 replies
Integer points on the line
Silverfalcon   8
N Feb 26, 2025 by SomeonecoolLovesMaths
A line passes through $ A(1,1)$ and $ B(100,1000)$. How many other points with integer coordinates are on the line and strictly between $ A$ and $ B$?

$ \textbf{(A)}\ 0\qquad \textbf{(B)}\ 2\qquad \textbf{(C)}\ 3\qquad \textbf{(D)}\ 8\qquad \textbf{(E)}\ 9$
8 replies
Silverfalcon
Nov 7, 2005
SomeonecoolLovesMaths
Feb 26, 2025
Integer points on the line
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Silverfalcon
5006 posts
#1 • 2 Y
Y by Adventure10, Mango247
A line passes through $ A(1,1)$ and $ B(100,1000)$. How many other points with integer coordinates are on the line and strictly between $ A$ and $ B$?

$ \textbf{(A)}\ 0\qquad \textbf{(B)}\ 2\qquad \textbf{(C)}\ 3\qquad \textbf{(D)}\ 8\qquad \textbf{(E)}\ 9$
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Shogia
107 posts
#2 • 2 Y
Y by Adventure10, Mango247
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JesusFreak197
1939 posts
#3 • 5 Y
Y by ahaanomegas, KLBBC, Adventure10, Mango247, and 1 other user
Note for this type of problem
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Silverfalcon
5006 posts
#4 • 1 Y
Y by Adventure10
Here is how I would do in this type
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Iversonfan2005
1697 posts
#5 • 2 Y
Y by Adventure10, Mango247
Click to reveal hidden text

EDIT: Forgot it was $\text{between}$ the points
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ahaanomegas
6294 posts
#6 • 1 Y
Y by Adventure10
JesusFreak197 wrote:
Note for this type of problem
Sorry for the revival, but this is a great fact which I've never heard of! Does anyone have a proof of this? Thanks in advance! :)
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talkinaway
5083 posts
#7 • 2 Y
Y by Adventure10, Mango247
There's a variant of this problem that pops up frequently, too - the question is if you have a $100 \times 1000$ cake sliced into square units, and you put one diagonal strip of red icing on the cake from the lower left to the lower right, how many square slices of cake get red icing?

I don't have the time right now to go through a rigorous proof, but the proof of that and the proof of "how many lattice points does the icing hit" are very similar. I think I did it one time here a LONG time ago (we're talking months, if not years) - it basically states that if you go from $(0,0)$ to $(p,q)$, with $p$ and $q$ relatively prime, you will NEVER hit a lattice point on the interior. You only get the two exterior lattice points.

Thus, if you go from $(0,0)$ to $(kp, kq)$, with $p, q$ relatively prime, then $k$ is the GCF of $kp$ and $kq$, and you hit an interior lattice point $k-1$ times - you repeat $p\times q$ rectangles, with the lattice points only coming there.

To get the number of slices of cake that get hit, you just examine each relatively prime rectangle, and note that there are $p + q$ slices that get hit, and you subtract off the endpoints.
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JustKeepRunning
2958 posts
#8 • 1 Y
Y by Adventure10
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This post has been edited 2 times. Last edited by JustKeepRunning, Jul 10, 2019, 11:28 AM
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SomeonecoolLovesMaths
3223 posts
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