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Nice inequalities
sealight2107   0
an hour ago
Problem: Let $a,b,c \ge 0$, $a+b+c=1$.Find the largest $k >0$ that satisfies:
$\sqrt{a+k(b-c)^2} + \sqrt{b+k(c-a)^2} + \sqrt{c+k(a-b)^2} \le \sqrt{3}$
0 replies
sealight2107
an hour ago
0 replies
Inequalities from SXTX
sqing   14
N an hour ago by MathBot101101
T702. Let $ a,b,c>0 $ and $ a+2b+3c=\sqrt{13}. $ Prove that $$ \sqrt{a^2+1} +2\sqrt{b^2+1} +3\sqrt{c^2+1} \geq 7$$S
T703. Let $ a,b $ be real numbers such that $ a+b\neq 0. $. Find the minimum of $ a^2+b^2+(\frac{1-ab}{a+b} )^2.$
T704. Let $ a,b,c>0 $ and $ a+b+c=3. $ Prove that $$ \frac{a^2+7}{(c+a)(a+b)} + \frac{b^2+7}{(a+b)(b+c)} +\frac{c^2+7}{(b+c)(c+a)}  \geq 6$$S
14 replies
sqing
Feb 18, 2025
MathBot101101
an hour ago
Number Theory
AnhQuang_67   3
N an hour ago by GreekIdiot
Source: HSGSO 2024
Let $p$ be an odd prime number and a sequence $\{a_n\}_{n=1}^{+\infty}$ satisfy $$a_1=1, a_2=2$$and $$a_{n+2}=2\cdot a_{n+1}+3\cdot a_n, \forall n \geqslant 1$$Prove that always exists positive integer $k$ satisfying for all positive integers $n$, then $a_n \ne k \mod{p}$.

P/s: $\ne$ is "not congruence"
3 replies
AnhQuang_67
2 hours ago
GreekIdiot
an hour ago
Solve All 6 IMO 2024 Problems (42/42), New Framework Looking for Feedback
Blackhole.LightKing   3
N an hour ago by DottedCaculator
Hi everyone,

I’ve been experimenting with a different way of approaching mathematical problem solving — a framework that emphasizes recursive structures and symbolic alignment rather than conventional step-by-step strategies.

Using this method, I recently attempted all six problems from IMO 2024 and was able to arrive at what I believe are valid full-mark solutions across the board (42/42 total score, by standard grading).

However, I don’t come from a formal competition background, so I’m sure there are gaps in clarity, communication, or even logic that I’m not fully aware of.

If anyone here is willing to take a look and provide feedback, I’d appreciate it — especially regarding:

The correctness and completeness of the proofs

Suggestions on how to make the ideas clearer or more elegant

Whether this approach has any broader potential or known parallels

I'm here to learn more and improve the presentation and thinking behind the work.

You can download the Solution here.

https://agi-origin.com/assets/pdf/AGI-Origin_IMO_2024_Solution.pdf


Thanks in advance,
— BlackholeLight0


3 replies
Blackhole.LightKing
4 hours ago
DottedCaculator
an hour ago
2 var inequalities
sqing   3
N an hour ago by sqing
Source: Own
Let $ a,b> 0 $ and $ a+b\leq  2ab . $ Prove that
$$ \frac{   a + b }{ a^2(1+ b^2)} \leq \sqrt 5-1$$$$ \frac{   a +ab+ b }{ a^2(1+ b^2)} \leq \frac{3(\sqrt5-1)}{2}$$$$ \frac{   a +a^2b^2+ b }{ a^2(1+ b^2)} \leq2$$Solution:
$a\ge\frac{b}{2b-1}, b>\frac12$ and $  \frac{   a +a^2b^2+ b }{ a^2(1+ b^2)} \le\frac{2ab+a^2b^2}{a^2(1+b^2)}=1+\frac{2b-a}{a(1+b^2)} \le 1+\frac{4b-3}{b^2+1}$

Assume $u=4b-3>0$ then $  \frac{   a +a^2b^2+ b }{ a^2(1+ b^2)}  \le 1+\frac{16u}{u^2+6u+25} =2+ \frac{16}{6+u+\frac{25}u} \le 3$
Equalityholds when $a=\frac{2}{3},b=2. $
3 replies
sqing
Yesterday at 1:13 PM
sqing
an hour ago
hard problem
Cobedangiu   8
N an hour ago by ReticulatedPython
Let $a,b,c>0$ and $a+b+c=3$. Prove that:
$\dfrac{4}{a+b}+\dfrac{4}{b+c}+\dfrac{4}{c+a} \le \dfrac{1}{a}+\dfrac{1}{b}+\dfrac{1}{c}+3$
8 replies
Cobedangiu
Apr 21, 2025
ReticulatedPython
an hour ago
Irrational equation
giangtruong13   3
N an hour ago by navier3072
Solve the equation : $$(\sqrt{x}+1)[2-(x-6)\sqrt{x-3}]=x+8$$
3 replies
giangtruong13
2 hours ago
navier3072
an hour ago
2 var inequalities
sqing   0
an hour ago
Source: Own
Let $ a,b> 0 $ and $ a+b\leq  3ab . $ Prove that
$$  \frac{ a + b }{ a^2(1+  3b^2)} \leq \frac{3}{2}$$$$  \frac{   a - ab+ b }{ a^2(1+ 3b^2)}  \leq 1$$$$ \frac{ a + 3ab+ b }{ a^2(1+  3b^2)}  \leq 3$$$$  \frac{   a -2ab+ b }{ a^2(1+ b^2)}\leq  \sqrt{\frac{5}{2}}-\frac{1}{2}$$$$ \frac{   a +ab+ b }{ a^2(1+ b^2)} \leq 2(\sqrt{10}-1)$$$$   \frac{   a -2a^2b^2+ b }{ a^2(1+ b^2)}\leq  \frac{\sqrt{82}-5}{2}$$
0 replies
sqing
an hour ago
0 replies
Non-negative real variables inequality
KhuongTrang   0
an hour ago
Source: own
Problem. Let $a,b,c\ge 0: ab+bc+ca>0.$ Prove that$$\color{blue}{\frac{\left(2ab+ca+cb\right)^{2}}{a^{2}+4ab+b^{2}}+\frac{\left(2bc+ab+ac\right)^{2}}{b^{2}+4bc+c^{2}}+\frac{\left(2ca+bc+ba\right)^{2}}{c^{2}+4ca+a^{2}}\ge \frac{8(ab+bc+ca)}{3}.}$$
0 replies
KhuongTrang
an hour ago
0 replies
circle geometry showing perpendicularity
Kyj9981   4
N an hour ago by cj13609517288
Two circles $\omega_1$ and $\omega_2$ intersect at points $A$ and $B$. A line through $B$ intersects $\omega_1$ and $\omega_2$ at points $C$ and $D$, respectively. Line $AD$ intersects $\omega_1$ at point $E \neq A$, and line $AC$ intersects $\omega_2$ at point $F \neq A$. If $O$ is the circumcenter of $\triangle AEF$, prove that $OB \perp CD$.
4 replies
Kyj9981
Mar 18, 2025
cj13609517288
an hour ago
Inequalities
sqing   20
N an hour ago by sqing
Let $ a,b,c> 0 $ and $ ab+bc+ca\leq  3abc . $ Prove that
$$ a+ b^2+c\leq a^2+ b^3+c^2 $$$$ a+ b^{11}+c\leq a^2+ b^{12}+c^2 $$
20 replies
sqing
Apr 22, 2025
sqing
an hour ago
Prove excircle is tangent to circumcircle
sarjinius   8
N 2 hours ago by Lyzstudent
Source: Philippine Mathematical Olympiad 2025 P4
Let $ABC$ be a triangle with incenter $I$, and let $D$ be a point on side $BC$. Points $X$ and $Y$ are chosen on lines $BI$ and $CI$ respectively such that $DXIY$ is a parallelogram. Points $E$ and $F$ are chosen on side $BC$ such that $AX$ and $AY$ are the angle bisectors of angles $\angle BAE$ and $\angle CAF$ respectively. Let $\omega$ be the circle tangent to segment $EF$, the extension of $AE$ past $E$, and the extension of $AF$ past $F$. Prove that $\omega$ is tangent to the circumcircle of triangle $ABC$.
8 replies
sarjinius
Mar 9, 2025
Lyzstudent
2 hours ago
Inequalities
hn111009   6
N Apr 6, 2025 by Arbelos777
Let $a,b,c>0$ satisfied $a^2+b^2+c^2=9.$ Find the minimum of $$P=\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}.$$
6 replies
hn111009
Apr 6, 2025
Arbelos777
Apr 6, 2025
Inequalities
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hn111009
55 posts
#1 • 1 Y
Y by PikaPika999
Let $a,b,c>0$ satisfied $a^2+b^2+c^2=9.$ Find the minimum of $$P=\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}.$$
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sqing
41809 posts
#2 • 1 Y
Y by hn111009
Let $ a,b,c>0 $ satisfied $a^2+b^2+c^2=9.$ Prove that $$\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}\geq 4 $$or
Let $ a,b,c>0 $ satisfied $a^2+b^2+c^2=1.$ Prove that $$\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}\geq 12 $$Good.
This post has been edited 2 times. Last edited by sqing, Apr 6, 2025, 2:28 AM
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hn111009
55 posts
#3
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sqing wrote:
Let $ a,b,c>0 $ satisfied $a^2+b^2+c^2=9.$ Prove that $$\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}\geq 4 $$Good.

Nice sir. Could you show the way you do!!
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James4623009
1 post
#4
Y by
This question can be solved by Euler's formula
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DAVROS
1662 posts
#5
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sqing wrote:
Let $ a,b,c>0 $ satisfied $a^2+b^2+c^2=9.$ Prove that $\dfrac{a}{bc}+\dfrac{2b}{ca}+\dfrac{5c}{ab}\geq 4 $
solution
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sqing
41809 posts
#6
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Very very nice.Thank DAVROS.
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Arbelos777
8 posts
#7
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That is correct.
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