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k a June Highlights and 2025 AoPS Online Class Information
jlacosta   0
Today at 3:57 PM
Congratulations to all the mathletes who competed at National MATHCOUNTS! If you missed the exciting Countdown Round, you can watch the video at this link. Are you interested in training for MATHCOUNTS or AMC 10 contests? How would you like to train for these math competitions in half the time? We have accelerated sections which meet twice per week instead of once starting on July 8th (7:30pm ET). These sections fill quickly so enroll today!

[list][*]MATHCOUNTS/AMC 8 Basics
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[*]AMC 10 Problem Series[/list]
For those interested in Olympiad level training in math, computer science, physics, and chemistry, be sure to enroll in our WOOT courses before August 19th to take advantage of early bird pricing!

Summer camps are starting this 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 a transformative 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)!

Be sure to mark your calendars for the following upcoming events:
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[*]June 9th, Monday, 7:30pm ET, Game Jam: Operation Shuffle!, Come join us to play our second round of Operation Shuffle! If you enjoy number sense, logic, and a healthy dose of luck, this is the game for you. No specific math background is required; all are welcome.[/list]
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0 replies
jlacosta
Today at 3:57 PM
0 replies
Original Problem on Logarithms
yes45   2
N 22 minutes ago by vincentwant
What is the value of $\log _{xyz}{n}$ if
$\log _{xy}{n} = 48$,
$\log _{yz}{n} = 64$, and
$\log _{z}{n} = 96$?

Answer

Solution
2 replies
yes45
Today at 3:09 PM
vincentwant
22 minutes ago
Find the value of pq+rs/ps+qr
Darealzolt   1
N 4 hours ago by vanstraelen
Let \(p,q,r,s\) be real numbers that satisfy
\[
p^2+q^2=r^2+s^2
\]\[
p^2+s^2-ps=q^2+r^2+qr
\]Hence find the value of \(\frac{pq+rs}{ps+qr}\)

Click to reveal hidden text
1 reply
Darealzolt
Yesterday at 3:40 AM
vanstraelen
4 hours ago
D1040 : A general and strange result
Dattier   1
N 4 hours ago by Dattier
Source: les dattes à Dattier
Let $f \in C([0,1];[0,1])$ bijective, $f(0)=0$ and $(a_k) \in [0,1]^\mathbb N$ with $ \sum \limits_{k=0}^{+\infty} a_k$ converge.

Is it true that $\sum \limits_{k=0}^{+\infty} \sqrt{f(a_k)\times f^{-1}(a_k)}$ converge?
1 reply
Dattier
May 31, 2025
Dattier
4 hours ago
Original Problem (Complex Numbers)
qrxz17   1
N 5 hours ago by sultanine
Problem: Given that for a complex number \(z\), the value of \(z \cdot \overline{z} +(z+\overline{z})\) is \(19\). Find all complex numbers \(z\).

Answer: Click to reveal hidden text

Solution: Writing the given equation in standard form, we get
\begin{align*}
        (a+bi)\cdot(a-bi) +[(a+bi)+(a-bi)] =a^2+b^2+2a.
    \end{align*}
Then we have
\begin{align*}
        a^2+b^2+2a &= 19 \\
        (a+1)^2+b^2 &=20
    \end{align*}
This is the standard equation of a circle. So, \(r^2=20\) and \(r=2\sqrt{5}\).

Therefore, the combined value of the sum and product of a complex number and its conjugate is \(19\) when the complex numbers lie on the circle centered at \((-1,0)\) with radius \(2\sqrt{5}\).
1 reply
qrxz17
Today at 3:18 PM
sultanine
5 hours ago
Daily Problem Writing Practice
KSH31415   2
N 5 hours ago by sultanine
I'm trying to get better at writing problems so I decided to challenge myself to write one problem for every day this month (June 2025). I will post them in this thread as well as edit this post with all of them in hide tags. If I can, I'll include a difficulty level in the form of AIME placement. If anybody wants to solve them and give feedback on the problem and/or my difficulty rating, please do!

June 1 (AIME P4)

June 1 (AIME P4)
A bag contains $6$ red balls and $6$ blue balls. A draw consists of randomly selecting $2$ of the remaining balls from bag without replacement, and then setting them aside. A draw is called a match if the two balls have the same color. Compute the expected number of draws until either a match occurs or the bag is empty.
2 replies
KSH31415
Today at 3:13 PM
sultanine
5 hours ago
functional equation in Z
Matheo_Lucas   2
N Today at 3:02 PM by mrtheory
Find all functions \( f : \mathbb{Z} \to \mathbb{Z} \) such that

\[
x f(2f(y) - x) + y^2 f(2x - f(y)) = \frac{f(x)^2}{x} + f(y f(y))
\]
for all \( x, y \in \mathbb{Z} \) with \( x \neq 0 \).
2 replies
Matheo_Lucas
Jan 11, 2025
mrtheory
Today at 3:02 PM
Recurrence trouble
SomeonecoolLovesMaths   4
N Today at 2:48 PM by Hello_Kitty
Let $0 < x_0 < y_0$ be real numbers. Define $x_{n+1} = \frac{x_n + y_n}{2}$ and $y_{n+1} = \sqrt{x_{n+1}y_n}$.
Prove that $\lim_{n \to \infty} x_n = \lim_{n \to \infty} y_n$ and hence find the limit.
4 replies
SomeonecoolLovesMaths
May 28, 2025
Hello_Kitty
Today at 2:48 PM
Functions
mclolikoi   3
N Today at 1:58 PM by Mathzeus1024
Let us consider f as the following function : $ f(x)= \frac {x - \sqrt{2}}{ [x  \sqrt{2} ] } $

1- Find the definition domain $ D_f $

2-Prove that $ f $ is continous on $ \sqrt{2} $

3-Study the continuity of $ f $ on $ \frac {3 \sqrt{2} }{2} $

4-Then draw the geometric representation of $ f $ on $ ] \frac {1}{ \sqrt{2} } ; 2 \sqrt{2} [ $
3 replies
mclolikoi
Sep 23, 2012
Mathzeus1024
Today at 1:58 PM
ISI UGB 2025
Entrepreneur   2
N Today at 1:46 PM by Hello_Kitty
Source: ISI UGB 2025
1.)
Suppose $f:\mathbb R\to\mathbb R$ is differentiable and $|f'(x)|<\frac 12\;\forall\;x\in\mathbb R.$ Show that for some $x_0\in\mathbb R,f(x_0)=x_0.$

3.)
Suppose $f:[0,1]\to\mathbb R$ is differentiable with $f(0)=0.$ If $|f'(x)|\le f(x)\;\forall\;x\in[0,1],$ then show that $f(x)=0\;\forall\;x.$

4.)
Let $S^1=\{z\in\mathbb C:|z|=1\}$ be the unit circle in the complex plane. Let $f:S^1\to S^1$ be the map given by $f(z)=z^2.$ We define $f^{(1)}:=f$ and $f^{(k+1)}=f\circ f^{(k)}$ for $k\ge 1.$ The smallest positive integer $n$ such that $f^n(z)=z$ is called period of $z.$ Determine the total number of points $S^1$ of period $2025.$

6.)
Let $\mathbb N$ denote the set of natural numbers, and let $(a_i,b_i), 1\le i\le 9,$ be nine distinct tuples in $\mathbb N\times\mathbb N.$ Show that there are $3$ distinct elements in the set $\{2^{a_i}3^{b_i}:1\le i\le 9\}$ whose product is a perfect cube.

8.)
Let $n\ge 2$ and let $a_1\le a_2\le\cdots\le a_n$ be positive integers such that $$\sum_{i=1}^n a_i=\prod_{i=1}^n a_i.$$Prove that $$\sum_{i=1}^n a_i\le 2n$$and determine when equality holds.
2 replies
Entrepreneur
May 27, 2025
Hello_Kitty
Today at 1:46 PM
functional analysis
ILOVEMYFAMILY   0
Today at 12:54 PM
Let $E$, $F$ be normed spaces with $E$ a Banach space. Suppose $\{A_n: E \to F\}$ is a family of continuous linear maps. Prove that the set
\[
X = \left\{ x \in E \mid \sup_{n\geq 1}|| A_n(x)||< +\infty  \right\}
\]is either of first category in $E$ or is equal to the whole space $E$.
0 replies
ILOVEMYFAMILY
Today at 12:54 PM
0 replies
Prove the statement
Butterfly   13
N Today at 9:35 AM by solyaris
Given an infinite sequence $\{x_n\} \subseteq  [0,1]$, there exists some constant $C$, for any $r>0$, among the sequence $x_n$ and $x_m$ could be chosen to satisfy $|n-m|\ge r $ and $|x_n-x_m|<\frac{C}{|n-m|}$.
13 replies
Butterfly
May 7, 2025
solyaris
Today at 9:35 AM
Limit problem
Martin.s   1
N Today at 7:47 AM by alexheinis
Find \(\lim_{n \to \infty} n \sin (2n! e \pi)\)
1 reply
Martin.s
Yesterday at 6:49 PM
alexheinis
Today at 7:47 AM
Putnam 1992 B1
sqrtX   2
N Today at 6:50 AM by de-Kirschbaum
Source: Putnam 1992
Let $S$ be a set of $n$ distinct real numbers. Let $A_{S}$ be the set of numbers that occur as averages of two distinct
elements of $S$. For a given $n \geq 2$, what is the smallest possible number of elements in $A_{S}$?
2 replies
sqrtX
Jul 18, 2022
de-Kirschbaum
Today at 6:50 AM
Expand into a Fourier series
Tip_pay   1
N Today at 1:39 AM by maths001Z
Expand the function in a Fourier series on the interval $(-\pi, \pi)$
$$f(x)=\begin{cases}
1, & -1<x\leq 0\\ 
x, & 0<x<1
\end{cases}$$
1 reply
Tip_pay
Dec 12, 2023
maths001Z
Today at 1:39 AM
right angle inside a rectangle wanted (HOMC 2018 Ind. p12)
parmenides51   2
N Feb 6, 2020 by sunken rock
Let ABCD be a rectangle with $45^o < \angle ADB < 60^o$. The diagonals $AC$ and$ BD$ intersect at $O$. A line passing through $O$ and perpendicular to $BD$ meets $AD$ and $CD$ at $M$ and $N$ respectively. Let $K$ be a point on side $BC$ such that $MK \parallel AC$. Show that $\angle MKN = 90^o$.
IMAGE
2 replies
parmenides51
Jan 31, 2020
sunken rock
Feb 6, 2020
right angle inside a rectangle wanted (HOMC 2018 Ind. p12)
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parmenides51
30653 posts
#1 • 2 Y
Y by TLH, Adventure10
Let ABCD be a rectangle with $45^o < \angle ADB < 60^o$. The diagonals $AC$ and$ BD$ intersect at $O$. A line passing through $O$ and perpendicular to $BD$ meets $AD$ and $CD$ at $M$ and $N$ respectively. Let $K$ be a point on side $BC$ such that $MK \parallel AC$. Show that $\angle MKN = 90^o$.
https://cdn.artofproblemsolving.com/attachments/4/1/1d37b96cebaea3409ade7ce6711ac2d3fc2ef9.png
This post has been edited 1 time. Last edited by parmenides51, Jan 31, 2020, 4:43 AM
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parmenides51
30653 posts
#2 • 1 Y
Y by Adventure10
posted for the image link
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sunken rock
4402 posts
#3 • 1 Y
Y by Adventure10
$BONC$ cyclic implies $MNKB$ cyclic, done!

Best regards,
sunken rock
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