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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.

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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
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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
J
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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
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Symmetric inequality
mrrobotbcmc   4
N 9 minutes ago by JARP091
Let a,b,c,d belong to positive real numbers such that a+b+c+d=1. Prove that a^3/(b+c)+b^3/(c+d)+c^3/(d+a)+d^3/(a+b)>=1/8
4 replies
mrrobotbcmc
an hour ago
JARP091
9 minutes ago
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Probably a good lemma
Zavyk09   4
N 42 minutes ago by Zavyk09
Source: found when solving exercises
Let $ABC$ be a triangle with circumcircle $\omega$. Arbitrary points $E, F$ on $AC, AB$ respectively. Circumcircle $\Omega$ of triangle $AEF$ intersects $\omega$ at $P \ne A$. $BE$ intersects $CF$ at $I$. $PI$ cuts $\Omega$ and $\omega$ at $K, L$ respectively. Construct parallelogram $KFRE$. Prove that $A, R, L$ are collinear.
4 replies
Zavyk09
Yesterday at 12:50 PM
Zavyk09
42 minutes ago
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Hard Inequality
JARP091   0
an hour ago
Source: Own?
Let \( a, b, c > 0 \) with \( abc = 1 \). Prove that
\[ \frac{a^5}{b^2 + 2c^3} + \frac{2b^5}{3c + a^6} + \frac{c^7}{a + b^4} \geq 2. \]
0 replies
JARP091
an hour ago
0 replies
J
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shade from tub
QueenArwen   1
N an hour ago by mikestro
Source: 46th International Tournament of Towns, Senior O-Level P4, Spring 2025
There was a tub on the plane, with its upper base greater that the lower one. The tub was overturned. Prove that the area of its visible shade did decrease. (The tub is a frustum of a right circular cone: its bases are two discs in parallel planes, such that their centers lie on a line perpendicular to these planes. The visible shade is the total shade besides the shade under the tub. Consider the sun rays as parallel.)
1 reply
QueenArwen
Mar 11, 2025
mikestro
an hour ago
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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
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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
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geometry
EeEeRUT   5
N 2 hours ago by MathLuis
Source: Thailand MO 2025 P4
Let $D,E$ and $F$ be touch points of the incenter of $\triangle ABC$ at $BC, CA$ and $AB$, respectively. Let $P,Q$ and $R$ be the circumcenter of triangles $AFE, BDF$ and $CED$, respectively. Show that $DP, EQ$ and $FR$ concurrent.
5 replies
EeEeRUT
May 13, 2025
MathLuis
2 hours ago
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Foot from vertex to Euler line
cjquines0   31
N 5 hours ago by awesomeming327.
Source: 2016 IMO Shortlist G5
Let $D$ be the foot of perpendicular from $A$ to the Euler line (the line passing through the circumcentre and the orthocentre) of an acute scalene triangle $ABC$. A circle $\omega$ with centre $S$ passes through $A$ and $D$, and it intersects sides $AB$ and $AC$ at $X$ and $Y$ respectively. Let $P$ be the foot of altitude from $A$ to $BC$, and let $M$ be the midpoint of $BC$. Prove that the circumcentre of triangle $XSY$ is equidistant from $P$ and $M$.
31 replies
cjquines0
Jul 19, 2017
awesomeming327.
5 hours ago
J
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Grand finale of 2021 Iberoamerican MO
jbaca   5
N Yesterday at 10:50 PM by MathLuis
Source: 2021 Iberoamerican Mathematical Olympiad, P6
Consider a $n$-sided regular polygon, $n \geq 4$, and let $V$ be a subset of $r$ vertices of the polygon. Show that if $r(r-3) \geq n$, then there exist at least two congruent triangles whose vertices belong to $V$.
5 replies
jbaca
Oct 20, 2021
MathLuis
Yesterday at 10:50 PM
J
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Geometry
AlexCenteno2007   1
N Yesterday at 9:05 PM by Diamond-jumper76
Let ABC be an acute triangle and A′
the point diametrically opposite A on the circumcircle of the triangle. Through point A, draw the tangent to the circumcircle of triangle ABC that intersects line BC at point D, and take a point E on segment BC such that AD = ED. Let A′′ be the point on the circumcircle of triangle ABC
(other than A) that lies between the reflection of line AA′
and line AE. Show that lines A′A′′ and BC are parallel.
1 reply
AlexCenteno2007
Yesterday at 8:33 PM
Diamond-jumper76
Yesterday at 9:05 PM
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f(x^3 + y^3 + z^3) = f(x)^3 + f(y)^3 + f(z)^3
pigfly   15
N Yesterday at 8:26 PM by MathIQ.
Source: VietNam TST 2005, problem 3
Find all functions $f: \mathbb{Z} \mapsto \mathbb{Z}$ satisfying the condition: $f(x^3 +y^3 +z^3 )=f(x)^3+f(y)^3+f(z)^3.$
15 replies
pigfly
Aug 4, 2004
MathIQ.
Yesterday at 8:26 PM
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geometry problem
invt   1
N Yesterday at 8:22 PM by Diamond-jumper76
In a triangle $ABC$ with $\angle B<\angle C$, denote its incenter and midpoint of $BC$ by $I$, $M$, respectively. Let $C'$ be the reflected point of $C$ wrt $AI$. Let the lines $MC'$ and $CI$ meet at $X$. Suppose that $\angle XAI=\angle XBI=90^{\circ}$. Prove that $\angle C=2\angle B$.
1 reply
invt
Saturday at 11:59 AM
Diamond-jumper76
Yesterday at 8:22 PM
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Gergonne point Harmonic quadrilateral
niwobin   3
N Yesterday at 7:51 PM by niwobin
Triangle ABC has incircle touching the sides at D, E, F as shown.
AD, BE, CF concurrent at Gergonne point G.
BG and CG cuts the incircle at X and Y, respectively.
AG cuts the incircle at K.
Prove: K, X, D, Y form a harmonic quadrilateral. (KX/KY = DX/DY)
3 replies
niwobin
Saturday at 8:17 PM
niwobin
Yesterday at 7:51 PM
J
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A "side chase" for juniors
Lukaluce   3
N Yesterday at 7:34 PM by lksb
Source: 2025 Junior Macedonian Mathematical Olympiad P5
Let $M$ be the midpoint of side $BC$ in $\triangle ABC$, and $P \neq B$ is such that the quadrilateral $ABMP$ is cyclic and the circumcircle of $\triangle BPC$ is tangent to the line $AB$. If $E$ is the second common point of the line $BP$ and the circumcircle of $\triangle ABC$, determine the ratio $BE: BP$.
3 replies
Lukaluce
Yesterday at 3:37 PM
lksb
Yesterday at 7:34 PM
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J
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I need help with this problem
VIATON   1
N Apr 18, 2025 by sqing
Let $x,y$ satisfy:
$\frac{4}{(x-1)^2 + (y-2)^2 +4} + \frac{9}{(x-2)^2 + (y-4)^2 +9} = 1$
$[(x-2)^2+(y-4)^2][ (x-1)^2 + (y-2)^2] = 36$
Find Max of :$x+y$
1 reply
VIATON
Apr 18, 2025
sqing
Apr 18, 2025
J
I need help with this problem
G H J
Reveal topic tags
algebra
Inequality
inequalities proposed
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VIATON
140 posts
VIATON
#1 h  Apr 18, 2025, 7:09 AM
Y by
Let $x,y$ satisfy:
$\frac{4}{(x-1)^2 + (y-2)^2 +4} + \frac{9}{(x-2)^2 + (y-4)^2 +9} = 1$
$[(x-2)^2+(y-4)^2][ (x-1)^2 + (y-2)^2] = 36$
Find Max of :$x+y$
This post has been edited 1 time. Last edited by VIATON, Apr 18, 2025, 7:09 AM
Reason: .
Z K Y
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sqing
42247 posts
sqing
#2 h  Apr 18, 2025, 2:20 PM
Y by
Let $ x,y $ be reals satisfy $\frac{4}{(x-1)^2 + (y-2)^2 +4} + \frac{9}{(x-2)^2 + (y-4)^2 +9} = 1 $ and $ [(x-2)^2+(y-4)^2][ (x-1)^2 + (y-2)^2] = 36. $ Prove that
$$0.749054...\leq x+y \leq 8.25095...$$*
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