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k a May Highlights and 2025 AoPS Online Class Information
jlacosta   0
May 1, 2025
May is an exciting month! National MATHCOUNTS is the second week of May in Washington D.C. and our Founder, Richard Rusczyk will be presenting a seminar, Preparing Strong Math Students for College and Careers, on May 11th.

Are you interested in working towards MATHCOUNTS and don’t know where to start? We have you covered! If you have taken Prealgebra, then you are ready for MATHCOUNTS/AMC 8 Basics. Already aiming for State or National MATHCOUNTS and harder AMC 8 problems? Then our MATHCOUNTS/AMC 8 Advanced course is for you.

Summer camps are starting next month at the Virtual Campus in math and language arts that are 2 - to 4 - weeks in duration. Spaces are still available - don’t miss your chance to have an enriching summer experience. There are middle and high school competition math camps as well as Math Beasts camps that review key topics coupled with fun explorations covering areas such as graph theory (Math Beasts Camp 6), cryptography (Math Beasts Camp 7-8), and topology (Math Beasts Camp 8-9)!

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[list][*]May 9th, 4:30pm PT/7:30pm ET, Casework 2: Overwhelming Evidence — A Text Adventure, a game where participants will work together to navigate the map, solve puzzles, and win! All are welcome.
[*]May 19th, 4:30pm PT/7:30pm ET, What's Next After Beast Academy?, designed for students finishing Beast Academy and ready for Prealgebra 1.
[*]May 20th, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 1 Math Jam, Problems 1 to 4, join the Canada/USA Mathcamp staff for this exciting Math Jam, where they discuss solutions to Problems 1 to 4 of the 2025 Mathcamp Qualifying Quiz!
[*]May 21st, 4:00pm PT/7:00pm ET, Mathcamp 2025 Qualifying Quiz Part 2 Math Jam, Problems 5 and 6, Canada/USA Mathcamp staff will discuss solutions to Problems 5 and 6 of the 2025 Mathcamp Qualifying Quiz![/list]
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0 replies
jlacosta
May 1, 2025
0 replies
Interesting inequality
sealight2107   4
N 42 minutes ago by NguyenVanHoa29
Source: Own
Let $a,b,c>0$ such that $a+b+c=3$. Find the minimum value of:
$Q=\frac{a}{b}+\frac{b}{c}+\frac{c}{a}+\frac{1}{a^3+b^3+abc}+\frac{1}{b^3+c^3+abc}+\frac{1}{c^3+a^3+abc}$
4 replies
sealight2107
May 6, 2025
NguyenVanHoa29
42 minutes ago
Inequality
nguyentlauv   3
N 43 minutes ago by NguyenVanHoa29
Source: Own
Let $a,b,c$ be positive real numbers such that $ab+bc+ca=3$ and $k\ge 0$, prove that
$$\frac{\sqrt{a+1}}{b+c+k}+\frac{\sqrt{b+1}}{c+a+k}+\frac{\sqrt{c+1}}{a+b+k} \geq \frac{3\sqrt{2}}{k+2}.$$
3 replies
nguyentlauv
May 6, 2025
NguyenVanHoa29
43 minutes ago
schur weighted
Ducksohappi   1
N an hour ago by truongngochieu
Schur-weighted:
let a,b,c be positive. Prove that:
$a^3+b^3+c^3+3abc\ge \sum ab\sqrt{a^2+b^2}$
1 reply
1 viewing
Ducksohappi
3 hours ago
truongngochieu
an hour ago
forced vertices in graphs
Davdav1232   1
N an hour ago by CBMaster
Source: Israel TST 7 2025 p2
Let \( G \) be a graph colored using \( k \) colors. We say that a vertex is forced if it has neighbors in all the other \( k - 1 \) colors.

Prove that for any \( 2024 \)-regular graph \( G \), there exists a coloring using \( 2025 \) colors such that at least \( 1013 \) of the colors have a forced vertex of that color.

Note: The graph coloring must be valid, this means no \( 2 \) vertices of the same color may be adjacent.
1 reply
Davdav1232
May 8, 2025
CBMaster
an hour ago
Mathematical expectation 1
Tricky123   3
N Yesterday at 1:13 PM by Tricky123
X is continuous random variable having spectrum
$(-\infty,\infty) $ and the distribution function is $F(x)$ then
$E(X)=\int_{0}^{\infty}(1-F(x)-F(-x))dx$ and find the expression of $V(x)$

Ans:- $V(x)=\int_{0}^{\infty}(2x(1-F(x)+F(-x))dx-m^{2}$

How to solve help me
3 replies
Tricky123
May 11, 2025
Tricky123
Yesterday at 1:13 PM
Derivative of unknown continuous function
smartvong   2
N Yesterday at 12:43 PM by solyaris
Source: UM Mathematical Olympiad 2024
Let $f: \mathbb{R} \to \mathbb{R}$ be a function whose derivative is continuous on $[0,1]$. Show that
$$\lim_{n \to \infty} \sum^n_{k = 1}\left[f\left(\frac{k}{n}\right) - f\left(\frac{2k - 1}{2n}\right)\right] = \frac{f(1) - f(0)}{2}.$$
2 replies
smartvong
Yesterday at 1:05 AM
solyaris
Yesterday at 12:43 PM
Divisibility of cyclic sum
smartvong   1
N Yesterday at 12:06 PM by alexheinis
Source: UM Mathematical Olympiad 2024
Let $n$ be a positive integer greater than $1$. Show that
$$4 \mid (x_1x_2 + x_2x_3 + \cdots + x_{n-1}x_n + x_nx_1 - n)$$where each of $x_1, x_2, \dots, x_n$ is either $1$ or $-1$.
1 reply
smartvong
Yesterday at 9:49 AM
alexheinis
Yesterday at 12:06 PM
Polynomial with integer coefficients
smartvong   1
N Yesterday at 10:04 AM by alexheinis
Source: UM Mathematical Olympiad 2024
Prove that there is no polynomial $f(x)$ with integer coefficients, such that $f(p) = \dfrac{p + q}{2}$ and $f(q) = \dfrac{p - q}{2}$ for some distinct primes $p$ and $q$.
1 reply
smartvong
Yesterday at 9:46 AM
alexheinis
Yesterday at 10:04 AM
Existence of scalars
smartvong   0
Yesterday at 9:44 AM
Source: UM Mathematical Olympiad 2024
Let $U$ be a finite subset of $\mathbb{R}$ such that $U = -U$. Let $f,g : \mathbb{R} \to \mathbb{R}$ be functions satisfying
$$g(x) - g(y ) = (x - y)f(x + y)$$for all $x,y \in \mathbb{R} \backslash U$.
Show that there exist scalars $\alpha, \beta, \gamma \in \mathbb{R}$ such that
$$f(x) = \alpha x + \beta$$for all $x \in \mathbb{R}$,
$$g(x) = \alpha x^2 + \beta x + \gamma$$for all $x \in \mathbb{R} \backslash U$.
0 replies
smartvong
Yesterday at 9:44 AM
0 replies
Invertible matrices in F_2
smartvong   1
N Yesterday at 9:02 AM by alexheinis
Source: UM Mathematical Olympiad 2024
Let $n \ge 2$ be an integer and let $\mathcal{S}_n$ be the set of all $n \times n$ invertible matrices in which their entries are $0$ or $1$. Let $m_A$ be the number of $1$'s in the matrix $A$. Determine the minimum and maximum values of $m_A$ in terms of $n$, as $A$ varies over $S_n$.
1 reply
smartvong
Yesterday at 12:41 AM
alexheinis
Yesterday at 9:02 AM
ISI UGB 2025 P3
SomeonecoolLovesMaths   13
N Yesterday at 8:29 AM by iced_tea
Source: ISI UGB 2025 P3
Suppose $f : [0,1] \longrightarrow \mathbb{R}$ is differentiable with $f(0) = 0$. If $|f'(x) | \leq f(x)$ for all $x \in [0,1]$, then show that $f(x) = 0$ for all $x$.
13 replies
SomeonecoolLovesMaths
May 11, 2025
iced_tea
Yesterday at 8:29 AM
Group Theory
Stephen123980   3
N Monday at 9:01 PM by BadAtMath23
Let G be a group of order $45.$ If G has a normal subgroup of order $9,$ then prove that $G$ is abelian without using Sylow Theorems.
3 replies
Stephen123980
May 9, 2025
BadAtMath23
Monday at 9:01 PM
calculus
youochange   2
N Monday at 7:46 PM by tom-nowy
$\int_{\alpha}^{\theta} \frac{d\theta}{\sqrt{cos\theta-cos\alpha}}$
2 replies
youochange
Monday at 2:26 PM
tom-nowy
Monday at 7:46 PM
ISI UGB 2025 P1
SomeonecoolLovesMaths   6
N Monday at 5:10 PM by SomeonecoolLovesMaths
Source: ISI UGB 2025 P1
Suppose $f \colon \mathbb{R} \longrightarrow \mathbb{R}$ is differentiable and $| f'(x)| < \frac{1}{2}$ for all $x \in \mathbb{R}$. Show that for some $x_0 \in \mathbb{R}$, $f \left( x_0 \right) = x_0$.
6 replies
SomeonecoolLovesMaths
May 11, 2025
SomeonecoolLovesMaths
Monday at 5:10 PM
Prove that EI bisects <BEC
TheMaskedMagician   2
N Jul 23, 2014 by SmartClown
Source: Saudi Arabia IMO TST Day II Problem 1
Let $\Gamma$ be a circle with center $O$ and $AE$ be a diameter. Point $D$ lies on segment $OE$ and point $B$ is the midpoint of one of the arcs $\widehat{AE}$ of $\Gamma$. Construct point $C$ such that $ABCD$ is a parallelogram. Lines $EB$ and $CD$ meet at $F$. Line $OF$ meets the minor arc $\widehat{EB}$ at $I$. Prove that $EI$ bisects $\angle BEC$.
2 replies
TheMaskedMagician
Jul 22, 2014
SmartClown
Jul 23, 2014
Prove that EI bisects <BEC
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Source: Saudi Arabia IMO TST Day II Problem 1
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TheMaskedMagician
2955 posts
#1 • 2 Y
Y by Adventure10, Mango247
Let $\Gamma$ be a circle with center $O$ and $AE$ be a diameter. Point $D$ lies on segment $OE$ and point $B$ is the midpoint of one of the arcs $\widehat{AE}$ of $\Gamma$. Construct point $C$ such that $ABCD$ is a parallelogram. Lines $EB$ and $CD$ meet at $F$. Line $OF$ meets the minor arc $\widehat{EB}$ at $I$. Prove that $EI$ bisects $\angle BEC$.
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infiniteturtle
1131 posts
#2 • 2 Y
Y by Adventure10, Mango247
Hmmm this is kind of sad.

Trivially $BCED, BFDO$ are cyclic. Let $\angle OBD =x$. Then we can easily get $ \angle BEC =\tfrac{\pi}{4}+x$ and $\angle EFI =\tfrac{\pi}{2}-x$. Since $AOI$ is isosceles $\angle AIO= \tfrac{\pi}{8}-\tfrac{x}{2}$ so $\angle FIE = \tfrac{3\pi}{8}+\tfrac{x}{2}$ so $\angle BEI =\tfrac{\pi}{8}+\tfrac{x}{2}=\tfrac{1}{2}\angle BEC$, as desired.

One can simply cram the angle measures into the diagram and be done with no effort.
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SmartClown
82 posts
#3 • 1 Y
Y by Adventure10
By simple angle chasing we get $BCED$ and $BFDO$ cyclic and then we just angle chase again.I think the problems in Saudi Arabia TST are too easy.
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