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k Funcional equation problem
khongphaiwminh   1
N an hour ago by jasperE3
Determine all functions $f \colon \mathbb R^+ \to \mathbb R^+$ that satisfy the equation
$$f(x+f(y))=f(x+y)+f(y)$$for any $x, y \in \mathbb R^+$. Note that $\mathbb R^+ \stackrel{\text{def}}{=} \{x \in \mathbb R \mid x > 0\}$.
1 reply
khongphaiwminh
an hour ago
jasperE3
an hour ago
AO and KI meet on $\Gamma$
Kayak   29
N an hour ago by Mathandski
Source: Indian TST 3 P2
Let $ABC$ be an acute-angled scalene triangle with circumcircle $\Gamma$ and circumcenter $O$. Suppose $AB < AC$. Let $H$ be the orthocenter and $I$ be the incenter of triangle $ABC$. Let $F$ be the midpoint of the arc $BC$ of the circumcircle of triangle $BHC$, containing $H$.

Let $X$ be a point on the arc $AB$ of $\Gamma$ not containing $C$, such that $\angle AXH = \angle AFH$. Let $K$ be the circumcenter of triangle $XIA$. Prove that the lines $AO$ and $KI$ meet on $\Gamma$.

Proposed by Anant Mudgal
29 replies
Kayak
Jul 17, 2019
Mathandski
an hour ago
4 Variables Cyclic Ineq
nataliaonline75   1
N an hour ago by NO_SQUARES
Prove that for every $x,y,z,w$ non-negative real numbers, then we have:
$\frac{x-y}{xy+2y+1}+\frac{y-z}{yz+2z+1} + \frac{z-w}{zw+2w+1} + \frac{w-x}{wx+2x+1} \geq 0$
1 reply
nataliaonline75
an hour ago
NO_SQUARES
an hour ago
IMO Genre Predictions
ohiorizzler1434   56
N an hour ago by Theoryman007
Everybody, with IMO upcoming, what are you predictions for the problem genres?


Personally I predict: predict
56 replies
ohiorizzler1434
May 3, 2025
Theoryman007
an hour ago
Number theory
MathsII-enjoy   2
N an hour ago by SimplisticFormulas
Prove that when $x^p+y^p$ | $(p^2-1)^n$ with $x,y$ are positive integers and $p$ is prime ($p>3$), we get: $x=y$
2 replies
MathsII-enjoy
Yesterday at 3:22 PM
SimplisticFormulas
an hour ago
National diophantine equation
KAME06   2
N an hour ago by damyan
Source: OMEC Ecuador National Olympiad Final Round 2024 N3 P5 day 2
Find all triples of non-negative integer numbers $(E, C, U)$ such that $EC \ge 1$ and:
$$2^{3^E}+3^{2^C}=593 \cdot 5^U$$
2 replies
KAME06
Feb 28, 2025
damyan
an hour ago
IMO ShortList 1998, number theory problem 1
orl   55
N an hour ago by reni_wee
Source: IMO ShortList 1998, number theory problem 1
Determine all pairs $(x,y)$ of positive integers such that $x^{2}y+x+y$ is divisible by $xy^{2}+y+7$.
55 replies
orl
Oct 22, 2004
reni_wee
an hour ago
Number of sets S
Jackson0423   2
N 2 hours ago by Jackson0423
Let \( S \) be a set consisting of non-negative integers such that:

1. \( 0 \in S \),
2. For any \( k \in S \), both \( k + 9 \in S \) and \( k + 10 \in S \).

Find the number of such sets \( S \).
2 replies
Jackson0423
2 hours ago
Jackson0423
2 hours ago
F.E....can you solve it?
Jackson0423   16
N 2 hours ago by jasperE3
Find all functions \( f : \mathbb{R} \to \mathbb{R} \) such that
\[
f\left(\frac{x^2 - f(x)}{f(x) - 1}\right) = x
\]for all real numbers \( x \) satisfying \( f(x) \neq 1 \).
16 replies
Jackson0423
Yesterday at 1:27 PM
jasperE3
2 hours ago
Find all positive a,b
shobber   14
N 2 hours ago by reni_wee
Source: APMO 2002
Find all positive integers $a$ and $b$ such that
\[ {a^2+b\over b^2-a}\quad\mbox{and}\quad{b^2+a\over a^2-b} \]
are both integers.
14 replies
shobber
Apr 8, 2006
reni_wee
2 hours ago
a