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Inequality involving square root cube root and 8th root
bamboozled   0
2 hours ago
If $a,b,c,d,e,f,g,h,k\in R^+$ and $a+b+c=d+e+f=g+h+k=8$, then find the minimum value of $\sqrt{ad^3 g^4} +\sqrt[3]{be^3 h^4} + \sqrt[8]{cf^3 k^4}$
0 replies
bamboozled
2 hours ago
0 replies
Old problem
kwin   2
N 2 hours ago by kwin
Let $a, b, c \ge 0$ and $ ab+bc+ca>0$. Prove that:
$$ \frac{1}{(a+b)^2} + \frac{1}{(b+c)^2} + \frac{1}{(c+a)^2} + \frac{15}{(a+b+c)^2} \ge \frac{6}{ab+bc+ca}$$Is there any generalizations?
2 replies
kwin
Sunday at 1:12 PM
kwin
2 hours ago
functional equation
henderson   4
N 2 hours ago by megarnie
Source: unknown
Find all functions $f :\mathbb{R^+}\to\mathbb{R^+}$, satisfying the condition

$f(1+xf(y))=yf(x+y)$

for any positive reals $x$ and $y$.
4 replies
henderson
Oct 8, 2015
megarnie
2 hours ago
Parallelograms and concyclicity
Lukaluce   31
N 2 hours ago by Ihatecombin
Source: EGMO 2025 P4
Let $ABC$ be an acute triangle with incentre $I$ and $AB \neq AC$. Let lines $BI$ and $CI$ intersect the circumcircle of $ABC$ at $P \neq B$ and $Q \neq C$, respectively. Consider points $R$ and $S$ such that $AQRB$ and $ACSP$ are parallelograms (with $AQ \parallel RB, AB \parallel QR, AC \parallel SP$, and $AP \parallel CS$). Let $T$ be the point of intersection of lines $RB$ and $SC$. Prove that points $R, S, T$, and $I$ are concyclic.
31 replies
Lukaluce
Apr 14, 2025
Ihatecombin
2 hours ago
My Unsolved FE in R+
ZeltaQN2008   2
N 2 hours ago by megarnie
Source: Ho Chi Minh TST 2017 - 2018
Find all functions $f:\mathbb{R}^+ \rightarrow \mathbb{R}^+$ such that for all any $x,y\in (0,\infty):$
$$f(1+xf(y))=yf(x+y)$$
2 replies
1 viewing
ZeltaQN2008
3 hours ago
megarnie
2 hours ago
Something nice
KhuongTrang   32
N 3 hours ago by arqady
Source: own
Problem. Given $a,b,c$ be non-negative real numbers such that $ab+bc+ca=1.$ Prove that

$$\sqrt{a+1}+\sqrt{b+1}+\sqrt{c+1}\le 1+2\sqrt{a+b+c+abc}.$$
32 replies
KhuongTrang
Nov 1, 2023
arqady
3 hours ago
Infimum of decreasing sequence b_n/n^2
a1267ab   35
N 3 hours ago by shendrew7
Source: USA Winter TST for IMO 2020, Problem 1 and TST for EGMO 2020, Problem 3, by Carl Schildkraut and Milan Haiman
Choose positive integers $b_1, b_2, \dotsc$ satisfying
\[1=\frac{b_1}{1^2} > \frac{b_2}{2^2} > \frac{b_3}{3^2} > \frac{b_4}{4^2} > \dotsb\]and let $r$ denote the largest real number satisfying $\tfrac{b_n}{n^2} \geq r$ for all positive integers $n$. What are the possible values of $r$ across all possible choices of the sequence $(b_n)$?

Carl Schildkraut and Milan Haiman
35 replies
a1267ab
Dec 16, 2019
shendrew7
3 hours ago
IMO Genre Predictions
ohiorizzler1434   52
N 3 hours ago by justaguy_69
Everybody, with IMO upcoming, what are you predictions for the problem genres?


Personally I predict: predict
52 replies
ohiorizzler1434
May 3, 2025
justaguy_69
3 hours ago
\sqrt{a^2+b^2+2}+\sqrt{b^2+c^2+2 }+\sqrt{c^2+a^2+2}\ge 6
parmenides51   19
N 4 hours ago by NicoN9
Source: JBMO Shortlist 2017 A1
Let $a, b, c$ be positive real numbers such that $a + b + c + ab + bc + ca + abc = 7$. Prove
that $\sqrt{a^2 + b^2 + 2 }+\sqrt{b^2 + c^2 + 2 }+\sqrt{c^2 + a^2 + 2 } \ge 6$ .
19 replies
parmenides51
Jul 25, 2018
NicoN9
4 hours ago
Inspired by Austria 2025
sqing   1
N 4 hours ago by sqing
Source: Own
Let $ a,b\geq 0 ,a,b\neq 1$ and $  a^2+b^2=1. $ Prove that$$   (a + b ) \left( \frac{a}{(b -1)^2} + \frac{b}{(a - 1)^2} \right) \geq 12+8\sqrt 2$$
1 reply
sqing
4 hours ago
sqing
4 hours ago
a