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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
A geometry problem involving 2 circles
Ujiandsd   0
9 minutes ago
Source: L
Point M is the midpoint of side BC of triangle ABC. The length of the radius of the outer circle of triangle ABM, triangle ACM
is 5 and 7 respectively find the distance between the center of their outer circles
0 replies
Ujiandsd
9 minutes ago
0 replies
Inequality, inequality, inequality...
Assassino9931   10
N 11 minutes ago by sqing
Source: Al-Khwarizmi Junior International Olympiad 2025 P6
Let $a,b,c$ be real numbers such that \[ab^2+bc^2+ca^2=6\sqrt{3}+ac^2+cb^2+ba^2.\]Find the smallest possible value of $a^2 + b^2 + c^2$.

Binh Luan and Nhan Xet, Vietnam
10 replies
2 viewing
Assassino9931
Yesterday at 9:38 AM
sqing
11 minutes ago
Grid with rooks
a_507_bc   3
N 15 minutes ago by TUAN2k8
Source: ARO Regional stage 2022 9.3
Given is a positive integer $n$. There are $2n$ mutually non-attacking rooks placed on a grid $2n \times 2n$. The grid is splitted into two connected parts, symmetric with respect to the center of the grid. What is the largest number of rooks that could lie in the same part?
3 replies
a_507_bc
Feb 16, 2023
TUAN2k8
15 minutes ago
IMO Shortlist 2013, Number Theory #3
lyukhson   47
N 18 minutes ago by cursed_tangent1434
Source: IMO Shortlist 2013, Number Theory #3
Prove that there exist infinitely many positive integers $n$ such that the largest prime divisor of $n^4 + n^2 + 1$ is equal to the largest prime divisor of $(n+1)^4 + (n+1)^2 +1$.
47 replies
lyukhson
Jul 10, 2014
cursed_tangent1434
18 minutes ago
Calculus
youochange   0
Yesterday at 5:39 PM
Find the area enclosed by the curves $e^x,e^{-x},x^2+y^2=1$

0 replies
youochange
Yesterday at 5:39 PM
0 replies
Another integral limit
RobertRogo   2
N Yesterday at 4:02 PM by Gauler
Source: "Traian Lalescu" student contest 2025, Section A, Problem 3
Let $f \colon [0, \infty) \to \mathbb{R}$ be a function differentiable at 0 with $f(0) = 0$. Find
$$\lim_{n \to \infty} \frac{1}{n} \int_{2^n}^{2^{n+1}} f\left(\frac{\ln x}{x}\right) dx$$
2 replies
RobertRogo
Friday at 2:28 PM
Gauler
Yesterday at 4:02 PM
Numerical methods problems
jjfgtuuu   0
Yesterday at 3:18 PM
Given that $x_1 = \dfrac{1}{\sqrt{2}}$, $x_2 = \dfrac{1}{\sqrt{6}}$, $x_3 = \dfrac{1}{\sqrt{8}}$, $x_4 = \dfrac{1}{\sqrt{10}}$.
Find the approximate value of $\mathrm{A} = \sum\limits_{i=1}^{4}x_i $ and its absolute and relative error, known that its absolute error is equal or lower than $10^{-5}.$
0 replies
jjfgtuuu
Yesterday at 3:18 PM
0 replies
Group Theory
Stephen123980   2
N Yesterday at 2:23 PM by BadAtMath23
Let G be a group of order $45.$ If G has a normal subgroup of order $9,$ then prove that $G$ is abelian without using Sylow Theorems.
2 replies
Stephen123980
Friday at 5:32 PM
BadAtMath23
Yesterday at 2:23 PM
Double integrals
fermion13pi   0
Yesterday at 1:58 PM
Source: Apostol, vol 2
Evaluate the double integral by converting to polar coordinates:

\[
\int_0^1 \int_{x^2}^x (x^2 + y^2)^{-1/2} \, dy \, dx
\]
Change the order of integration and then convert to polar coordinates.

0 replies
fermion13pi
Yesterday at 1:58 PM
0 replies
D1028 : A strange result about linear algebra
Dattier   0
Yesterday at 1:49 PM
Source: les dattes à Dattier
Let $p>3$ a prime number, with $H \subset M_p(\mathbb R), \dim(H)\geq 2$ and $H-\{0\} \subset GL_p(\mathbb R)$, $H$ vector space.

Is it true that $H-\{0\}$ is a group?
0 replies
Dattier
Yesterday at 1:49 PM
0 replies
Preparing for Putnam level entrance examinations
Cats_on_a_computer   4
N Yesterday at 1:16 PM by Cats_on_a_computer
Non American high schooler in the equivalent of grade 12 here. Where I live, two the best undergraduates program in the country accepts students based on a common entrance exam. The first half of the exam is “screening”, with 4 options being presented per question, each of which one has to assign a True or False. This first half is about the difficulty of an average AIME, or JEE Adv paper, and it is a requirement for any candidate to achieve at least 24/40 on this half for the examiners to even consider grading the second part. The second part consists of long form questions, and I have, no joke, seen them literally rip off, verbatim, Putnam A6s. Some of the problems are generally standard textbook problems in certain undergrad courses but obviously that doesn’t translate it to being doable for high school students. I’ve effectively got to prepare for a slightly nerfed Putnam, if you will, and so I’ve been looking for resources (not just problems) for Putnam level questions. Does anyone have any suggestions?
4 replies
Cats_on_a_computer
Friday at 8:32 AM
Cats_on_a_computer
Yesterday at 1:16 PM
Marginal Profit
NC4723   1
N Yesterday at 10:09 AM by Juno_34
Please help me solve this
1 reply
NC4723
Dec 11, 2015
Juno_34
Yesterday at 10:09 AM
Romania NMO 2023 Grade 11 P1
DanDumitrescu   15
N Yesterday at 5:46 AM by anudeep
Source: Romania National Olympiad 2023
Determine twice differentiable functions $f: \mathbb{R} \rightarrow \mathbb{R}$ which verify relation

\[
    \left( f'(x) \right)^2 + f''(x) \leq 0, \forall x \in \mathbb{R}.
    \]
15 replies
DanDumitrescu
Apr 14, 2023
anudeep
Yesterday at 5:46 AM
Subset Ordered Pairs of {1, 2, ..., 10}
ahaanomegas   11
N Yesterday at 5:27 AM by cappucher
Source: Putnam 1990 A6
If $X$ is a finite set, let $X$ denote the number of elements in $X$. Call an ordered pair $(S,T)$ of subsets of $ \{ 1, 2, \cdots, n \} $ $ \emph {admissible} $ if $ s > |T| $ for each $ s \in S $, and $ t > |S| $ for each $ t \in T $. How many admissible ordered pairs of subsets $ \{ 1, 2, \cdots, 10 \} $ are there? Prove your answer.
11 replies
ahaanomegas
Jul 12, 2013
cappucher
Yesterday at 5:27 AM
ratio chasing in a square, isosceles triangle
parmenides51   2
N Mar 19, 2021 by parmenides51
Source: 2005 Kyiv TST3 8.3 9.2 for Ukraine MO
Let $ABCD$ be a square, point $E$ lies on the side $CD$, $O$ be the center of the square, $N$ be the midpoint of $BC$, $P=BE \cap NO$. It is known that $\vartriangle POE$ is isosceles. In what ratio does the point $E$ divide the side of the square $CD$?.

(Klurman O.)
2 replies
parmenides51
Mar 16, 2021
parmenides51
Mar 19, 2021
ratio chasing in a square, isosceles triangle
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G H BBookmark kLocked kLocked NReply
Source: 2005 Kyiv TST3 8.3 9.2 for Ukraine MO
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parmenides51
30652 posts
#1 • 3 Y
Y by Mango247, Mango247, Mango247
Let $ABCD$ be a square, point $E$ lies on the side $CD$, $O$ be the center of the square, $N$ be the midpoint of $BC$, $P=BE \cap NO$. It is known that $\vartriangle POE$ is isosceles. In what ratio does the point $E$ divide the side of the square $CD$?.

(Klurman O.)
This post has been edited 3 times. Last edited by parmenides51, Mar 16, 2021, 9:58 PM
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franzliszt
23531 posts
#2
Y by
parmenides51 wrote:
Let $ABCD$ be a square, point $E$ lies on the side $CD$, $O$ be the center of the square, $N$ be the midpoint of $BC$, $P=BE \cap NO$. It is known that $\vartriangle POE$ is isosceles. In what ratio does the point $E$ divide the side of the square $CD$?.

(Klurman O.)

Doesn't this only happen if $E=C$?
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parmenides51
30652 posts
#3
Y by
there is another one case
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