Happy Memorial Day! Please note that AoPS Online is closed May 24-26th.

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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
Hard Functional Equation in the Complex Numbers
yaybanana   5
N 7 minutes ago by aaravdodhia
Source: Own
Find all functions $f:\mathbb {C}\rightarrow \mathbb {C}$, s.t :

$f(xf(y)) + f(x^2+y) = f(x+y)x + f(f(y))$

for all $x,y \in \mathbb{C}$
5 replies
yaybanana
Apr 9, 2025
aaravdodhia
7 minutes ago
Power tower sum
Rijul saini   9
N 22 minutes ago by ihategeo_1969
Source: India IMOTC 2024 Day 3 Problem 2
Let $a$ and $n$ be positive integers such that:
1. $a^{2^n}-a$ is divisible by $n$,
2. $\sum\limits_{k=1}^{n} k^{2024}a^{2^k}$ is not divisible by $n$.

Prove that $n$ has a prime factor smaller than $2024$.

Proposed by Shantanu Nene
9 replies
Rijul saini
May 31, 2024
ihategeo_1969
22 minutes ago
Nice "if and only if" function problem
ICE_CNME_4   7
N 25 minutes ago by ICE_CNME_4
Let $f : [0, \infty) \to [0, \infty)$, $f(x) = \dfrac{ax + b}{cx + d}$, with $a, d \in (0, \infty)$, $b, c \in [0, \infty)$. Prove that there exists $n \in \mathbb{N}^*$ such that for every $x \geq 0$
\[
f_n(x) = \frac{x}{1 + nx}, \quad \text{if and only if } f(x) = \frac{x}{1 + x}, \quad \forall x \geq 0.
\](For $n \in \mathbb{N}^*$ and $x \geq 0$, the notation $f_n(x)$ represents $\underbrace{(f \circ f \circ \dots \circ f)}_{n \text{ times}}(x)$. )

Please do it at 9th grade level. Thank you!
7 replies
ICE_CNME_4
Yesterday at 7:23 PM
ICE_CNME_4
25 minutes ago
Cauchy-Schwarz 2
prtoi   8
N 25 minutes ago by mrtheory
Source: Handout by Samin Riasat
if $a^2+b^2+c^2+d^2=4$, prove that:
$\frac{a^2}{b}+\frac{b^2}{c}+\frac{c^2}{d}+\frac{d^2}{a}\ge4$
8 replies
prtoi
Mar 26, 2025
mrtheory
25 minutes ago
No more topics!
Polynomial
EtacticToe   3
N Apr 2, 2025 by EmersonSoriano
Source: Own
Let $f(x)$ be a monic polynomial with integer coefficient. And suppose there exist 4 distinct integer $a,b,c,d$ such that $f(a)=…=f(d)=5$.

Find all $k$ such that $f(k)=8$
3 replies
EtacticToe
Dec 14, 2024
EmersonSoriano
Apr 2, 2025
Polynomial
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EtacticToe
82 posts
#1
Y by
Let $f(x)$ be a monic polynomial with integer coefficient. And suppose there exist 4 distinct integer $a,b,c,d$ such that $f(a)=…=f(d)=5$.

Find all $k$ such that $f(k)=8$
This post has been edited 1 time. Last edited by EtacticToe, Dec 14, 2024, 6:44 PM
Reason: The row
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RagvaloD
4918 posts
#2
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$f(x)=(x-a)(x-b)(x-c)(x-d)g(x)+5$
$f(k)=(k-a)(k-b)(k-c)(k-d)g(k)+5=8 \to (k-a)(k-b)(k-c)(k-d) | 3$
But as $k-a,k-b,k-c,k-d$ should be different integers, there is no such $k$
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yuribogomolov
1 post
#3
Y by
Quote:
RagvaloD wrote:
there is no such k

3 has four integer divisors (-3, -1, 1, 3).
Z K Y
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EmersonSoriano
47 posts
#4
Y by
yuribogomolov wrote:
Quote:
RagvaloD wrote:
there is no such k

3 has four integer divisors (-3, -1, 1, 3).

But it would have to be fulfilled that the product of those four integers is a divisor of 3, which cannot happen, since the product of those four numbers would be 9.
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