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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.

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[*]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
k i Adding contests to the Contest Collections
dcouchman   1
N Apr 5, 2023 by v_Enhance
Want to help AoPS remain a valuable Olympiad resource? Help us add contests to AoPS's Contest Collections.

Find instructions and a list of contests to add here: https://artofproblemsolving.com/community/c40244h1064480_contests_to_add
1 reply
dcouchman
Sep 9, 2019
v_Enhance
Apr 5, 2023
k i Zero tolerance
ZetaX   49
N May 4, 2019 by NoDealsHere
Source: Use your common sense! (enough is enough)
Some users don't want to learn, some other simply ignore advises.
But please follow the following guideline:


To make it short: ALWAYS USE YOUR COMMON SENSE IF POSTING!
If you don't have common sense, don't post.


More specifically:

For new threads:


a) Good, meaningful title:
The title has to say what the problem is about in best way possible.
If that title occured already, it's definitely bad. And contest names aren't good either.
That's in fact a requirement for being able to search old problems.

Examples:
Bad titles:
- "Hard"/"Medium"/"Easy" (if you find it so cool how hard/easy it is, tell it in the post and use a title that tells us the problem)
- "Number Theory" (hey guy, guess why this forum's named that way¿ and is it the only such problem on earth¿)
- "Fibonacci" (there are millions of Fibonacci problems out there, all posted and named the same...)
- "Chinese TST 2003" (does this say anything about the problem¿)
Good titles:
- "On divisors of a³+2b³+4c³-6abc"
- "Number of solutions to x²+y²=6z²"
- "Fibonacci numbers are never squares"


b) Use search function:
Before posting a "new" problem spend at least two, better five, minutes to look if this problem was posted before. If it was, don't repost it. If you have anything important to say on topic, post it in one of the older threads.
If the thread is locked cause of this, use search function.

Update (by Amir Hossein). The best way to search for two keywords in AoPS is to input
[code]+"first keyword" +"second keyword"[/code]
so that any post containing both strings "first word" and "second form".


c) Good problem statement:
Some recent really bad post was:
[quote]$lim_{n\to 1}^{+\infty}\frac{1}{n}-lnn$[/quote]
It contains no question and no answer.
If you do this, too, you are on the best way to get your thread deleted. Write everything clearly, define where your variables come from (and define the "natural" numbers if used). Additionally read your post at least twice before submitting. After you sent it, read it again and use the Edit-Button if necessary to correct errors.


For answers to already existing threads:


d) Of any interest and with content:
Don't post things that are more trivial than completely obvious. For example, if the question is to solve $x^{3}+y^{3}=z^{3}$, do not answer with "$x=y=z=0$ is a solution" only. Either you post any kind of proof or at least something unexpected (like "$x=1337, y=481, z=42$ is the smallest solution). Someone that does not see that $x=y=z=0$ is a solution of the above without your post is completely wrong here, this is an IMO-level forum.
Similar, posting "I have solved this problem" but not posting anything else is not welcome; it even looks that you just want to show off what a genius you are.

e) Well written and checked answers:
Like c) for new threads, check your solutions at least twice for mistakes. And after sending, read it again and use the Edit-Button if necessary to correct errors.



To repeat it: ALWAYS USE YOUR COMMON SENSE IF POSTING!


Everything definitely out of range of common sense will be locked or deleted (exept for new users having less than about 42 posts, they are newbies and need/get some time to learn).

The above rules will be applied from next monday (5. march of 2007).
Feel free to discuss on this here.
49 replies
ZetaX
Feb 27, 2007
NoDealsHere
May 4, 2019
Inequality
Sadigly   7
N a minute ago by MITDragon
Source: Azerbaijan Junior MO 2025 P5
For positive real numbers $x;y;z$ satisfying $0<x,y,z<2$, find the biggest value the following equation could acquire:


$$(2x-yz)(2y-zx)(2z-xy)$$
7 replies
+1 w
Sadigly
May 9, 2025
MITDragon
a minute ago
Minimum value of a 3 variable expression
bin_sherlo   5
N a minute ago by Primeniyazidayi
Source: Türkiye 2025 JBMO TST P6
Find the minimum value of
\[\frac{x^3+1}{(y-1)(z+1)}+\frac{y^3+1}{(z-1)(x+1)}+\frac{z^3+1}{(x-1)(y+1)}\]where $x,y,z>1$ are reals.
5 replies
bin_sherlo
Yesterday at 7:16 PM
Primeniyazidayi
a minute ago
Nice R+ FE
math_comb01   5
N 4 minutes ago by jasperE3
Source: XOOK 2025 P3
Find all functions $f : \mathbb{R}_{>0} \to \mathbb{R}_{>0}$ so that for any $x, y \in \mathbb{R}_{>0}$, we have \[ f(xf(x^2)+yf(x))=xf(y+xf(x)). \]
Proposed by Anmol Tiwari and MathLuis
5 replies
math_comb01
Feb 9, 2025
jasperE3
4 minutes ago
2n^2+4n-1 and 3n+4 have common powers
bin_sherlo   3
N 9 minutes ago by Primeniyazidayi
Source: Türkiye 2025 JBMO TST P5
Find all positive integers $n$ such that a positive integer power of $2n^2+4n-1$ equals to a positive integer power of $3n+4$.
3 replies
bin_sherlo
Yesterday at 7:13 PM
Primeniyazidayi
9 minutes ago
Help me solve this problem please. Thank you so much!
illybest   1
N 17 minutes ago by GreekIdiot
Give two fixed points B and C, and point A moving on the circle (O). Let D be a point on (O) such that AD is perpendicular to BC. Let O' be the point symmetric to O with respect to BC, M be the midpoint of BC, and N ( dinstinct from D) be the intersection of MD with the circumcircle of triangle AOD. Suppose DO' intersects the circle (O) again at S.
a) Prove that the circle (OMN) is tangent to the circle (DNS)
b) Let d be the line tangent to (DNS) at N. Prove that d always passes through a fixed point when A moves along the arc BC of (O)
1 reply
illybest
Sep 8, 2024
GreekIdiot
17 minutes ago
Looks like power mean, but it is not
Nuran2010   6
N 31 minutes ago by sqing
Source: Azerbaijan Al-Khwarizmi IJMO TST 2025
For $a,b,c$ positive real numbers satisfying $a^2+b^2+c^2 \geq 3$,show that:

$\sqrt[3]{\frac{a^3+b^3+c^3}{3}}+\frac{a+b+c}{9} \geq \frac{4}{3}$.
6 replies
Nuran2010
Yesterday at 11:51 AM
sqing
31 minutes ago
Expressing polynomial as product of two polynomials
Sadigly   5
N 34 minutes ago by Sadigly
Source: Azerbaijan Senior NMO 2021
Define $P(x)=((x-a_1)(x-a_2)...(x-a_n))^2 +1$, where $a_1,a_2...,a_n\in\mathbb{Z}$ and $n\in\mathbb{N^+}$. Prove that $P(x)$ couldn't be expressed as product of two non-constant polynomials with integer coefficients.
5 replies
Sadigly
Yesterday at 9:10 PM
Sadigly
34 minutes ago
Simple inequality
sqing   19
N an hour ago by sqing
Source: Old? Where?
Let $a,b,c$ be positive real numbers .Prove that
$$(a+b)^2+(a+b+4c)^2\geq \frac{100 abc}{a+b+c}$$
19 replies
sqing
Jan 16, 2021
sqing
an hour ago
Interesting inequalities
sqing   2
N an hour ago by sqing
Source: Own
Let $ a,b>0  $ . Prove that
$$ \frac{a^2+b^2}{ab+1}+ \frac{4}{ (\sqrt{a}+\sqrt{b})^2} \geq 2$$$$ \frac{a^2+b^2}{ab+1}+ \frac{3}{a+\sqrt{ab}+b} \geq 2$$$$  \frac{a^3+b^3}{ab+1}+ \frac{4}{(a+b)^2}  \geq 2$$$$  \frac{a^3+b^3}{ab+1}+ \frac{3}{a^2+ab+b^2}  \geq 2$$$$\frac{a^2+b^2}{ab+2}+ \frac{1}{2\sqrt{ab}}  \geq \frac{2+3\sqrt{2}-2\sqrt{2(\sqrt{2}-1)}}{4} $$
2 replies
sqing
Today at 4:34 AM
sqing
an hour ago
Interesting inequalities
sqing   9
N an hour ago by sqing
Source: Own
Let $ a,b,c\geq 0 , (a+k )(b+c)=k+1.$ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}\geq  \frac{2k-3+2\sqrt{k+1}}{3k-1}$$Where $ k\geq \frac{2}{3}.$
Let $ a,b,c\geq 0 , (a+1)(b+c)=2.$ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}\geq 2\sqrt{2}-1$$Let $ a,b,c\geq 0 , (a+3)(b+c)=4.$ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}\geq  \frac{7}{4}$$Let $ a,b,c\geq 0 , (3a+2)(b+c)= 5.$ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}\geq  \frac{2(2\sqrt{15}-5)}{3}$$
9 replies
sqing
May 10, 2025
sqing
an hour ago
Small Combinatorics Problem by Macharstein
macharstein   0
an hour ago
Alice and Bob are playing a two-turn game on an infinite grid. Alice goes first. In every cell, she places an arrow pointing in one of the four directions: up, down, left, or right. Then goes Bob. He puts $K$ robots, each in a different cell.
From this configuration the robots start moving: every second, each robot moves one step in the direction of the arrow in its current cell. If two robots land on the same cell at the same time, they merge into one.
Bob wins if the robots end up in the same row or same column infinitely many times.
Find all values of $K$ for which Alice can always prevent Bob from winning, no matter where he puts the robots.
0 replies
macharstein
an hour ago
0 replies
Shortest number theory you might've seen in your life
AlperenINAN   7
N 2 hours ago by Assassino9931
Source: Turkey JBMO TST 2025 P4
Let $p$ and $q$ be prime numbers. Prove that if $pq(p+1)(q+1)+1$ is a perfect square, then $pq + 1$ is also a perfect square.
7 replies
AlperenINAN
Yesterday at 7:51 PM
Assassino9931
2 hours ago
Help me this problem. Thank you
illybest   2
N 2 hours ago by GreekIdiot
Find f: R->R such that
f( xy + f(z) ) = (( xf(y) + yf(x) )/2) + z
2 replies
illybest
4 hours ago
GreekIdiot
2 hours ago
It just wants you to factorize 47 factorial
Sadigly   1
N 2 hours ago by pooh123
Source: Azerbaijan Senior NMO 2021
At least how many numbers must be deleted from the product $1 \times 2 \times \dots \times 46 \times 47$ in order to make it a perfect square?
1 reply
Sadigly
Yesterday at 9:00 PM
pooh123
2 hours ago
Find the distance
Rushil   6
N Jul 18, 2024 by SomeonecoolLovesMaths
Source: Indian RMO 1993 Problem 1
Let $ABC$ be an acute angled triangle and $CD$ be the altitude through $C$. If $AB = 8$ and $CD = 6$, find the distance between the midpoints of $AD$ and $BC$.
6 replies
Rushil
Oct 15, 2005
SomeonecoolLovesMaths
Jul 18, 2024
Find the distance
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G H BBookmark kLocked kLocked NReply
Source: Indian RMO 1993 Problem 1
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Rushil
1592 posts
#1 • 3 Y
Y by Adventure10, Adventure10, Mango247
Let $ABC$ be an acute angled triangle and $CD$ be the altitude through $C$. If $AB = 8$ and $CD = 6$, find the distance between the midpoints of $AD$ and $BC$.
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frt
1294 posts
#2 • 3 Y
Y by ajaykharabe, Adventure10, Mango247
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AlastorMoody
2125 posts
#3 • 2 Y
Y by Adventure10, Mango247
Let $X,Y,Z$ be mid-points of $BC,AD,AC$ respectively $\implies XZ||AB \text{  and  } XZ=\frac{1}{2}AB=4$
By further angle chasing, it is evident that $CD \perp XZ$ and since, $\Delta CZD$ and $\Delta CDX$ are isosceles $\implies CZDX $ is a kite,
Therefore, Let $CD \cap XZ =O \implies CO=DO=\frac{1}{2}CD=6 $ and we also know, $\Delta DXB$ is isosceles
Therefore, if $XH$ is altitude of $\Delta XDB$ ,such, $H \in AB \implies DO=XH=3$ .........Let $OX=x \implies OZ=4-x$
By midpoint theorem, $$OZ=YD=4-x \text{ and since, XODH is rectangle, } \implies OX=DH=4-x \implies YH=4$$Therefore, $$XY=\sqrt{XH^2+YH^2}=\boxed{5}$$
This post has been edited 1 time. Last edited by AlastorMoody, Nov 6, 2018, 8:17 PM
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Kuroshio
72 posts
#4
Y by
An easier solution.

Let $E$ and $F$ be the midpoints of $AD$ and $BC$ respectively
we have to find $EF$
Draw $FG$ $\perp$ $AB$ with $G$ on $AB$.
$FG = \frac{1}{2} CD =3$
Observe that $AD + BD=8
\implies ED+DG=4 => EG = 4$
In right angled $\Delta EFG$,
$EF =\sqrt{3^2 + 4^2}= 5$
This post has been edited 5 times. Last edited by Kuroshio, Jul 14, 2020, 6:16 AM
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ATGY
2502 posts
#5 • 2 Y
Y by Mango247, Mango247
Let F be the midpoint of BC, let G be the midpoint of BD, let E be the midpoint of AD.

Notice that $EG = ED + GD = \frac{1}{2}(AD + BD) = 4$.

Also, $FG = \frac{1}{2}CD = 3$ by the Midpoint Theorem.

Since $\triangle{FGB} \sim \triangle{CDB}$, $\angle{FGB} = \angle{FGD} = 90^{\circ}$. Hence $\triangle{FGE}$ is a right triangle.
$$\implies EF = \sqrt{EG^2 + FG^2 } = \boxed{5} ~ \text{by the Pythagorean Theorem}$$
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SomeonecoolLovesMaths
3254 posts
#6 • 1 Y
Y by SatisfiedMagma
Let $A = (0,0)$, $B=(8,0)$, $C = (x,6)$, $D = (x,0)$. Thus Midpoint of $AD = \left( \frac{x}{2},0 \right)$ and midpoint of $BC = \left( \frac{x+8}{6},0 \right)$. Using distance formula we get $\boxed{5}$.
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SomeonecoolLovesMaths
3254 posts
#7
Y by
Another beautiful construction, I don't know if someone has done it that way or not.

Construct $B`$ such that $A,B,D,B`$ are collinear. Let $M$ be the midpoint of $AD$, thus it is also the midpoint of $BB`$. Now $DB` = 8$ and $CD = 6$. By pythagorean theorem, $B`C = 10$. And using MPT, the required answer is $\boxed{5}$.
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