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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
Probably a good lemma
Zavyk09   4
N a few seconds ago by Zavyk09
Source: found when solving exercises
Let $ABC$ be a triangle with circumcircle $\omega$. Arbitrary points $E, F$ on $AC, AB$ respectively. Circumcircle $\Omega$ of triangle $AEF$ intersects $\omega$ at $P \ne A$. $BE$ intersects $CF$ at $I$. $PI$ cuts $\Omega$ and $\omega$ at $K, L$ respectively. Construct parallelogram $KFRE$. Prove that $A, R, P$ are collinear.
4 replies
Zavyk09
Yesterday at 12:50 PM
Zavyk09
a few seconds ago
Hard Inequality
JARP091   0
11 minutes ago
Source: Own?
Let \( a, b, c > 0 \) with \( abc = 1 \). Prove that
\[
\frac{a^5}{b^2 + 2c^3} + \frac{2b^5}{3c + a^6} + \frac{c^7}{a + b^4} \geq 2.
\]
0 replies
JARP091
11 minutes ago
0 replies
Symmetric inequality
mrrobotbcmc   2
N 14 minutes ago by JARP091
Let a,b,c,d belong to positive real numbers such that a+b+c+d=1. Prove that a^3/(b+c)+b^3/(c+d)+c^3/(d+a)+d^3/(a+b)>=1/8
2 replies
mrrobotbcmc
39 minutes ago
JARP091
14 minutes ago
shade from tub
QueenArwen   1
N 21 minutes ago by mikestro
Source: 46th International Tournament of Towns, Senior O-Level P4, Spring 2025
There was a tub on the plane, with its upper base greater that the lower one. The tub was overturned. Prove that the area of its visible shade did decrease. (The tub is a frustum of a right circular cone: its bases are two discs in parallel planes, such that their centers lie on a line perpendicular to these planes. The visible shade is the total shade besides the shade under the tub. Consider the sun rays as parallel.)
1 reply
QueenArwen
Mar 11, 2025
mikestro
21 minutes ago
Cool Integral, Cooler Solution
Existing_Human1   3
N Yesterday at 8:21 PM by MathIQ.
Source: https://youtu.be/YO38MCdj-GM?si=DCn6DaQTeX8RXhl0
$$\int_{0}^{\infty} \! e^{-x^2}\cos(5x) \,dx$$
Bonus points if you can do it without Feynman
3 replies
Existing_Human1
May 6, 2025
MathIQ.
Yesterday at 8:21 PM
Unsolving differential equation
Madunglecha   0
Yesterday at 3:33 PM
For parameter t
I made a differential equation :
y"=y*(x')^2
for here, '&" is derivate and second order derivate for t
could anyone tell me what is equation between y&x?
0 replies
Madunglecha
Yesterday at 3:33 PM
0 replies
Expanding tan z?
ys-lg   1
N Yesterday at 9:10 AM by alexheinis
How to expand $\tan z$ by residue theorem? Should by something like
\[[z^n]\tan z\propto\oint _{|z|=N}\frac{\tan z}{z^{n+1}}\mathrm dz\]where $N$ tends to infty, but I'm not sure about details.
1 reply
ys-lg
Yesterday at 6:46 AM
alexheinis
Yesterday at 9:10 AM
2013 Japan MO Finals
parkjungmin   0
Yesterday at 9:09 AM
If there's anyone who's good at math

Please solve this problem
0 replies
parkjungmin
Yesterday at 9:09 AM
0 replies
Double integration
Tricky123   1
N Yesterday at 4:44 AM by greenturtle3141
Q)
\[\iint_{R} \sin(xy) \,dx\,dy, \quad R = \left[0, \frac{\pi}{2}\right] \times \left[0, \frac{\pi}{2}\right]\]
How to solve the problem like this I am using the substitution method but its seems like very complicated in the last
Please help me
1 reply
Tricky123
Yesterday at 3:51 AM
greenturtle3141
Yesterday at 4:44 AM
Proving a group is abelian
dragosgamer12   9
N Yesterday at 12:43 AM by ysharifi
Source: Florin Stanescu, Gazeta Matematica seria B Nr.2/2025
Let $(G,\cdot)$ be a group, $K$ a subgroup of $G$ and $f : G \rightarrow G$ an endomorphism with the following property:
There exists a nonempty set $H\subset	G$ such that for any $k \in G \setminus K$ there exist $h  \in H$ with $f(h)=k$ and $z \cdot h= h \cdot z$, for any $z \in H$.

a)Prove that $(G, \cdot)$ is abelian.
b)If, additionally, $H$ is a subgroup of $G$, prove that $H=G$
9 replies
dragosgamer12
May 15, 2025
ysharifi
Yesterday at 12:43 AM
Problem on distinct prime divisors of P(1),...,P(n)
IAmTheHazard   3
N Saturday at 7:04 PM by IAmTheHazard
Find all nonnegative real numbers $\lambda$ such that there exists an integer polynomial $P$ with no integer roots and a constant $c>0$ such that
$$\prod_{i=1}^n P(i)=P(1)\cdot P(2)\cdots P(n)$$has at least $cn^{\lambda}$ distinct prime divisors for all positive integers $n$.
3 replies
IAmTheHazard
Apr 4, 2025
IAmTheHazard
Saturday at 7:04 PM
Invertible Matrices
Mateescu Constantin   7
N Saturday at 6:27 PM by CHOUKRI
Source: Romanian District Olympiad 2018 - Grade XI - Problem 1
Show that if $n\ge 2$ is an integer, then there exist invertible matrices $A_1, A_2, \ldots, A_n \in \mathcal{M}_2(\mathbb{R})$ with non-zero entries such that:

\[A_1^{-1} + A_2^{-1} + \ldots + A_n^{-1} = (A_1 + A_2 + \ldots + A_n)^{-1}.\]
Edit.
7 replies
Mateescu Constantin
Mar 10, 2018
CHOUKRI
Saturday at 6:27 PM
A challenging sum
Polymethical_   2
N Saturday at 6:19 PM by GreenKeeper
I tried to integrate series of log(1-x) / x
2 replies
Polymethical_
May 17, 2025
GreenKeeper
Saturday at 6:19 PM
Analytic on C excluding countably many points
Omid Hatami   12
N Saturday at 6:13 PM by alinazarboland
Source: IMS 2009
Let $ A\subset \mathbb C$ be a closed and countable set. Prove that if the analytic function $ f: \mathbb C\backslash A\longrightarrow \mathbb C$ is bounded, then $ f$ is constant.
12 replies
Omid Hatami
May 20, 2009
alinazarboland
Saturday at 6:13 PM
Combinatorics game
VicKmath7   3
N Apr 12, 2025 by Topiary
Source: First JBMO TST of France 2020, Problem 1
Players A and B play a game. They are given a box with $n=>1$ candies. A starts first. On a move, if in the box there are $k$ candies, the player chooses positive integer $l$ so that $l<=k$ and $(l, k) =1$, and eats $l$ candies from the box. The player who eats the last candy wins. Who has winning strategy, in terms of $n$.
3 replies
VicKmath7
Mar 4, 2020
Topiary
Apr 12, 2025
Combinatorics game
G H J
G H BBookmark kLocked kLocked NReply
Source: First JBMO TST of France 2020, Problem 1
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VicKmath7
1390 posts
#1 • 3 Y
Y by MathsMadman, mathematicsy, cubres
Players A and B play a game. They are given a box with $n=>1$ candies. A starts first. On a move, if in the box there are $k$ candies, the player chooses positive integer $l$ so that $l<=k$ and $(l, k) =1$, and eats $l$ candies from the box. The player who eats the last candy wins. Who has winning strategy, in terms of $n$.
This post has been edited 2 times. Last edited by VicKmath7, Mar 11, 2020, 11:19 AM
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Taha1381
816 posts
#2 • 2 Y
Y by MathsMadman, cubres
For odd $n$ the first player chooses $n-2$ candies and eat them so he wins(except for $n=1$ where he obviously wins).for even $n$ first player should take odd number of candies so he will become second player and $n$ will be odd.So first player wins iff $n \equiv 1 \pmod 2$.
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wizixez
168 posts
#3 • 1 Y
Y by cubres
Easy:::
There are two cases:::
$\boxed{1}n$ is odd number.

LEMMA:For odd $n$ ,$(n,n-2)=1$
Using that the first player eats $n-2$ candles there are $2$ candles remained.Second eats 1 and first eats the last one and wins.

$\boxed{2}n$ is even.
Notice First player should and will take an odd number of candles.Now second player continues to the game as first player and takes $n-k-2$ candles and wins...
So:::
$\mathcal{WINNER}=\begin{cases}First\to n=2k+1\\
Second\to n=2k\end{cases}$
$\boxed{\lambda}$
Z K Y
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Topiary
25 posts
#4 • 1 Y
Y by cubres
We claim that the first player will win iff $n \equiv 1 \pmod 2$, and the second player winning for even $n$. The first player clearly wins for $n =1$, and for odd $n\ge 1$ they simply take $n-2$ candies with there being $2$ left. The second player eats one and thus the first player wins.
For even $n$ the first player takes an odd number of candies due to the nature of the game. This results in the second player playing with the first instance of odd $n$. This results in them winning.
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