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Advanced topics in Inequalities
va2010   9
N 2 hours ago by Strangett
So a while ago, I compiled some tricks on inequalities. You are welcome to post solutions below!
9 replies
va2010
Mar 7, 2015
Strangett
2 hours ago
24 Aug FE problem
nicky-glass   3
N 2 hours ago by pco
Source: Baltic Way 1995
$f:\mathbb R\setminus \{0\} \to \mathbb R$
(i) $f(1)=1$,
(ii) $\forall x,y,x+y \neq 0:f(\frac{1}{x+y})=f(\frac{1}{x})+f(\frac{1}{y}) : P(x,y)$
(iii) $\forall x,y,x+y \neq 0:(x+y)f(x+y)=xyf(x)f(y) :Q(x,y)$
$f=?$
3 replies
nicky-glass
Aug 24, 2016
pco
2 hours ago
Simply equation but hard
giangtruong13   1
N 2 hours ago by anduran
Find all integer pairs $(x,y)$ satisfy that: $$(x^2+y)(y^2+x)=(x-y)^3$$
1 reply
giangtruong13
4 hours ago
anduran
2 hours ago
Hard Polynomial Problem
MinhDucDangCHL2000   1
N 3 hours ago by Tung-CHL
Source: IDK
Let $P(x)$ be a polynomial with integer coefficients. Suppose there exist infinitely many integer pairs $(a,b)$ such that $P(a) + P(b) = 0$. Prove that the graph of $P(x)$ is symmetric about a point (i.e., it has a center of symmetry).
1 reply
MinhDucDangCHL2000
4 hours ago
Tung-CHL
3 hours ago
IMO LongList 1985 CYP2 - System of Simultaneous Equations
Amir Hossein   13
N 3 hours ago by cubres
Solve the system of simultaneous equations
\[\sqrt x - \frac 1y - 2w + 3z = 1,\]\[x + \frac{1}{y^2} - 4w^2 - 9z^2 = 3,\]\[x \sqrt x - \frac{1}{y^3} - 8w^3 + 27z^3 = -5,\]\[x^2 + \frac{1}{y^4} - 16w^4 - 81z^4 = 15.\]
13 replies
Amir Hossein
Sep 10, 2010
cubres
3 hours ago
Centroid Distance Identity in Triangle
zeta1   5
N 3 hours ago by DottedCaculator
Let M be any point inside triangle ABC, and let G be the centroid of triangle ABC. Prove that:

\[
|MA|^2 + |MB|^2 + |MC|^2 = |GA|^2 + |GB|^2 + |GC|^2 + 3|MG|^2
\]
5 replies
zeta1
Today at 12:28 PM
DottedCaculator
3 hours ago
Numbers not power of 5
Kayak   34
N 3 hours ago by cursed_tangent1434
Source: Indian TST D1 P2
Show that there do not exist natural numbers $a_1, a_2, \dots, a_{2018}$ such that the numbers \[ (a_1)^{2018}+a_2, (a_2)^{2018}+a_3, \dots, (a_{2018})^{2018}+a_1 \]are all powers of $5$

Proposed by Tejaswi Navilarekallu
34 replies
Kayak
Jul 17, 2019
cursed_tangent1434
3 hours ago
Number Theory Chain!
JetFire008   58
N 3 hours ago by Primeniyazidayi
I will post a question and someone has to answer it. Then they have to post a question and someone else will answer it and so on. We can only post questions related to Number Theory and each problem should be more difficult than the previous. Let's start!

Question 1
58 replies
JetFire008
Apr 7, 2025
Primeniyazidayi
3 hours ago
Silly Sequences
whatshisbucket   25
N 4 hours ago by bin_sherlo
Source: ELMO 2018 #2, 2018 ELMO SL N3
Consider infinite sequences $a_1,a_2,\dots$ of positive integers satisfying $a_1=1$ and $$a_n \mid a_k+a_{k+1}+\dots+a_{k+n-1}$$for all positive integers $k$ and $n.$ For a given positive integer $m,$ find the maximum possible value of $a_{2m}.$

Proposed by Krit Boonsiriseth
25 replies
whatshisbucket
Jun 28, 2018
bin_sherlo
4 hours ago
Divisibility NT FE
CHESSR1DER   12
N 4 hours ago by internationalnick123456
Source: Own
Find all functions $f$ $N \rightarrow N$ such for any $a,b$:
$(a+b)|a^{f(b)} + b^{f(a)}$.
12 replies
CHESSR1DER
Apr 14, 2025
internationalnick123456
4 hours ago
a