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Tech support and questions about AoPS classes and materials
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Inequality
Sappat   10
N an hour ago by iamnotgentle
Let $a,b,c$ be real numbers such that $a^2+b^2+c^2=1$. Prove that
$\frac{a^2}{1+2bc}+\frac{b^2}{1+2ca}+\frac{c^2}{1+2ab}\geq\frac{3}{5}$
10 replies
Sappat
Feb 7, 2018
iamnotgentle
an hour ago
ISI UGB 2025 P4
SomeonecoolLovesMaths   9
N 2 hours ago by nyacide
Source: ISI UGB 2025 P4
Let $S^1 = \{ z \in \mathbb{C} \mid |z| =1 \}$ be the unit circle in the complex plane. Let $f \colon S^1 \longrightarrow S^2$ be the map given by $f(z) = z^2$. We define $f^{(1)} \colon = f$ and $f^{(k+1)} \colon = f \circ f^{(k)}$ for $k \geq 1$. The smallest positive integer $n$ such that $f^{(n)}(z) = z$ is called the period of $z$. Determine the total number of points in $S^1$ of period $2025$.
(Hint : $2025 = 3^4 \times 5^2$)
9 replies
SomeonecoolLovesMaths
May 11, 2025
nyacide
2 hours ago
Self-evident inequality trick
Lukaluce   9
N 2 hours ago by sqing
Source: 2025 Junior Macedonian Mathematical Olympiad P4
Let $x, y$, and $z$ be positive real numbers, such that $x^2 + y^2 + z^2 = 3$. Prove the inequality
\[\frac{x^3}{2 + x} + \frac{y^3}{2 + y} + \frac{z^3}{2 + z} \ge 1.\]When does the equality hold?
9 replies
Lukaluce
Yesterday at 3:34 PM
sqing
2 hours ago
Prove n is square-free given divisibility condition
CatalanThinker   1
N 2 hours ago by CatalanThinker
Source: 1995 Indian Mathematical Olympiad
Let \( n \) be a positive integer such that \( n \) divides the sum
\[
1 + \sum_{i=1}^{n-1} i^{n-1}.
\]Prove that \( n \) is square-free.
1 reply
CatalanThinker
3 hours ago
CatalanThinker
2 hours ago
Inspired by SXJX (12)2022 Q1167
sqing   0
2 hours ago
Source: Own
Let $ a,b,c>0 $. Prove that$$\frac{kabc-1} {abc(a+b+c+8(2k-1))}\leq \frac{1}{16 }$$Where $ k>\frac{1}{2}.$
0 replies
sqing
2 hours ago
0 replies
What is thiss
EeEeRUT   5
N 2 hours ago by MathLuis
Source: Thailand MO 2025 P6
Find all function $f: \mathbb{R}^+ \rightarrow \mathbb{R}$,such that the inequality $$f(x) + f\left(\frac{y}{x}\right) \leqslant \frac{x^3}{y^2} + \frac{y}{x^3}$$holds for all positive reals $x,y$ and for every positive real $x$, there exist positive reals $y$, such that the equality holds.
5 replies
EeEeRUT
May 14, 2025
MathLuis
2 hours ago
Thailand geometry
EeEeRUT   4
N 2 hours ago by MathLuis
Source: Thailand MO 2025 P7
Let $ABC$ be a triangle with $AB < AC$. The tangent to the circumcircle of $\triangle ABC$ at $A$ intersects $BC$ at $D$. The angle bisector of $\angle BAC$ intersect $BC$ at $E$. Suppose that the perpendicular bisector of $AE$ intersect $AB, AC$ at $P,Q$, respectively. Show that $$\sqrt{\frac{BP}{CQ}} = \frac{AC \cdot BD}{AB \cdot CD}$$
4 replies
EeEeRUT
May 14, 2025
MathLuis
2 hours ago
JBMO Shortlist 2021 G2
Lukaluce   10
N 2 hours ago by Adventure1000
Source: JBMO Shortlist 2021
Let $P$ be an interior point of the isosceles triangle $ABC$ with $\hat{A} = 90^{\circ}$. If
$$\widehat{PAB} + \widehat{PBC} + \widehat{PCA} = 90^{\circ},$$prove that $AP \perp BC$.

Proposed by Mehmet Akif Yıldız, Turkey
10 replies
Lukaluce
Jul 2, 2022
Adventure1000
2 hours ago
Thailand MO 2025 P3
Kaimiaku   5
N 2 hours ago by MathLuis
Let $a,b,c,x,y,z$ be positive real numbers such that $ay+bz+cx \le az+bx+cy$. Prove that $$ \frac{xy}{ax+bx+cy}+\frac{yz}{by+cy+az}+\frac{zx}{cz+az+bx} \le \frac{x+y+z}{a+b+c}$$
5 replies
Kaimiaku
May 13, 2025
MathLuis
2 hours ago
Simple inequality
sqing   7
N 3 hours ago by sqing
Source: 2016 China Sichuan High School Mathematics Competition ,Q14
Let $a, b, c$ are positive real numbers .Show that$$abc\geq \frac{a+b+c}{\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2}}\geq (b+c-a)(c+a-b)(a+b-c)$$
7 replies
sqing
May 22, 2016
sqing
3 hours ago
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