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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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SL 2015 G1: Prove that IJ=AH
Problem_Penetrator   137
N 17 minutes ago by heheman
Source: IMO 2015 Shortlist, G1
Let $ABC$ be an acute triangle with orthocenter $H$. Let $G$ be the point such that the quadrilateral $ABGH$ is a parallelogram. Let $I$ be the point on the line $GH$ such that $AC$ bisects $HI$. Suppose that the line $AC$ intersects the circumcircle of the triangle $GCI$ at $C$ and $J$. Prove that $IJ = AH$.
137 replies
Problem_Penetrator
Jul 7, 2016
heheman
17 minutes ago
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IMO Shortlist 2011, G2
WakeUp   30
N 35 minutes ago by ezpotd
Source: IMO Shortlist 2011, G2
Let $A_1A_2A_3A_4$ be a non-cyclic quadrilateral. Let $O_1$ and $r_1$ be the circumcentre and the circumradius of the triangle $A_2A_3A_4$. Define $O_2,O_3,O_4$ and $r_2,r_3,r_4$ in a similar way. Prove that
\[\frac{1}{O_1A_1^2-r_1^2}+\frac{1}{O_2A_2^2-r_2^2}+\frac{1}{O_3A_3^2-r_3^2}+\frac{1}{O_4A_4^2-r_4^2}=0.\]

Proposed by Alexey Gladkich, Israel
30 replies
WakeUp
Jul 13, 2012
ezpotd
35 minutes ago
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2-var inequality
sqing   1
N an hour ago by sqing
Source: Own
Let $ a,b\geq 0 ,\frac{a}{b+2}+\frac{b}{a+2}+ \frac{ab}{3}\leq 1.$ Prove that
$$ a^2+b^2 +\frac{5}{3}ab \leq 4$$
1 reply
sqing
an hour ago
sqing
an hour ago
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Rational Points in n-Dimensional Space
steven_zhang123   0
2 hours ago
Let \( T = (x_1, x_2, \ldots, x_n) \), where \( x_i \) is rational for \( i = 1, 2, \ldots, n \). A vector \( T \) is called a rational point in \( n \)-dimensional space. Denote the set of all such vectors \( T \) as \( S \). For \( A = (x_1, x_2, \ldots, x_n) \) and \( B = (y_1, y_2, \ldots, y_n) \) in \( S \), define the distance between points \( A \) and \( B \) as \( d(A, B) = \sqrt{(x_1 - y_1)^2 + (x_2 - y_2)^2 + \cdots + (x_n - y_n)^2} \). We say that point \( A \) can move to point \( B \) if and only if there is a unit distance between two points in \( S \).

Prove:
(1) If \( n \leq 4 \), there exists a point that cannot be reached from the origin via a finite number of moves.
(2) If \( n \geq 5 \), any point in \( S \) can be reached from any other point via moves.
0 replies
steven_zhang123
2 hours ago
0 replies
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Inspired by old results
sqing   5
N 2 hours ago by sqing
Source: Own
Let $a,b,c $ be reals such that $a^2+b^2+c^2=3$ .Prove that
$$(1-a)(k-b)(1-c)+abc\ge -k$$Where $ k\geq 1.$
$$(1-a)(1-b)(1-c)+abc\ge -1$$$$(1-a)(1-b)(1-c)-abc\ge -\frac{1}{2}-\sqrt 2$$
5 replies
sqing
Yesterday at 7:36 AM
sqing
2 hours ago
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equation in integers
Pirkuliyev Rovsen   2
N 2 hours ago by ytChen
Solve in $Z$ the equation $a^2+b=b^{2022}$
2 replies
Pirkuliyev Rovsen
Feb 10, 2025
ytChen
2 hours ago
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Inequality for Sequences
steven_zhang123   0
3 hours ago
Given a positive number \( t \) and integers \( m, n \geq 2 \), prove that for any \( n \) positive numbers \( a_1, a_2, \ldots, a_n \) satisfying \( a_j - a_{j-1} \leq t \) for \( j = 1, 2, \ldots, n \) (with the convention \( a_0 = 0 \)), the following inequality holds:
\[ \sum_{j=1}^n a_j^{2m-1} \leq \frac{mt}{2} \left( \sum_{j=1}^n a_j^{m-1} \right)^2. \]
0 replies
steven_zhang123
3 hours ago
0 replies
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Circumcircle of ADM
v_Enhance   70
N 4 hours ago by Shan3t
Source: USA TSTST 2012, Problem 7
Triangle $ABC$ is inscribed in circle $\Omega$. The interior angle bisector of angle $A$ intersects side $BC$ and $\Omega$ at $D$ and $L$ (other than $A$), respectively. Let $M$ be the midpoint of side $BC$. The circumcircle of triangle $ADM$ intersects sides $AB$ and $AC$ again at $Q$ and $P$ (other than $A$), respectively. Let $N$ be the midpoint of segment $PQ$, and let $H$ be the foot of the perpendicular from $L$ to line $ND$. Prove that line $ML$ is tangent to the circumcircle of triangle $HMN$.
70 replies
v_Enhance
Jul 19, 2012
Shan3t
4 hours ago
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Prove this relation in triangle ABC
Entrepreneur   1
N 4 hours ago by MathIQ.
Source: Conjectured by me
In $\Delta ABC,$ prove that$$\color{blue}{2\angle A=3\angle B\implies c^3a^3(c+a)^2=b^2(c^2+a^2-b^2+2ca)(c^2+a^2-b^2)^2.}$$
1 reply
Entrepreneur
Aug 1, 2024
MathIQ.
4 hours ago
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45 degrees everywhere
Rijul saini   12
N 4 hours ago by guptaamitu1
Source: India IMOTC 2024 Day 2 Problem 2
Let $ABC$ be an acute angled triangle with $AC>AB$ and incircle $\omega$. Let $\omega$ touch the sides $BC, CA,$ and $AB$ at $D, E,$ and $F$ respectively. Let $X$ and $Y$ be points outside $\triangle ABC$ satisfying \[\angle BDX = \angle XEA = \angle YDC = \angle AFY = 45^{\circ}.\]Prove that the circumcircles of $\triangle AXY, \triangle AEF$ and $\triangle ABC$ meet at a point $Z\ne A$.

Proposed by Atul Shatavart Nadig and Shantanu Nene
12 replies
Rijul saini
May 31, 2024
guptaamitu1
4 hours ago
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equation 2025
mohamed-adam   1
N 4 hours ago by MathIQ.
Source: own
Find all positive integers $a,b$ such that $$a^8-2b^5=2025b$$
1 reply
mohamed-adam
Yesterday at 7:49 PM
MathIQ.
4 hours ago
J
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Graph Theory
ABCD1728   1
N 4 hours ago by ABCD1728
Can anyone provide the PDF version of "Graphs: an introduction" by Radu Bumbacea (XYZ press), thanks!
1 reply
ABCD1728
Yesterday at 5:10 AM
ABCD1728
4 hours ago
J
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Rectangles of grid cells
tapir1729   11
N 4 hours ago by Mathandski
Source: TSTST 2024, problem 9
Let $n \ge 2$ be a fixed integer. The cells of an $n \times n$ table are filled with the integers from $1$ to $n^2$ with each number appearing exactly once. Let $N$ be the number of unordered quadruples of cells on this board which form an axis-aligned rectangle, with the two smaller integers being on opposite vertices of this rectangle. Find the largest possible value of $N$.

Anonymous
11 replies
tapir1729
Jun 24, 2024
Mathandski
4 hours ago
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Interesting problem from a friend
v4913   11
N 5 hours ago by YaoAOPS
Source: I'm not sure...
Let the incircle $(I)$ of $\triangle{ABC}$ touch $BC$ at $D$, $ID \cap (I) = K$, let $\ell$ denote the line tangent to $(I)$ through $K$. Define $E, F \in \ell$ such that $\angle{EIF} = 90^{\circ}, EI, FI \cap (AEF) = E', F'$. Prove that the circumcenter $O$ of $\triangle{ABC}$ lies on $E'F'$.
11 replies
v4913
Nov 25, 2023
YaoAOPS
5 hours ago
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Number Theory
TUAN2k8   4
N Apr 19, 2025 by vsamc
Prove that there are infinitely many of positive integers m such that $m+1 | 3^m+1$
4 replies
TUAN2k8
Apr 18, 2025
vsamc
Apr 19, 2025
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Number Theory
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Reveal topic tags
fun nt
number theory
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TUAN2k8
30 posts
TUAN2k8
#1 h  Apr 18, 2025, 3:25 PM
Y by
Prove that there are infinitely many of positive integers m such that $m+1 | 3^m+1$
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Roger.Moore
5 posts
Roger.Moore
#2 h  Apr 18, 2025, 6:06 PM
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TUAN2k8
30 posts
TUAN2k8
#3 h  Apr 18, 2025, 11:08 PM
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Any solution?
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epl1
157 posts
epl1
#4 h  Apr 19, 2025, 2:44 AM
Y by
Woah, self made?
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vsamc
3789 posts
vsamc
#5 h  Apr 19, 2025, 2:51 AM • 2 Y
Y by kiyoras_2001, centslordm
$m = 3^{3^k}$ works for all $k\geq 0$, since $$3^{3^k} + 1 \mid (3^{3^k})^{3^{3^k-k}} + 1^{3^{3^k-k}} = 3^{3^{3^k}} + 1.$$
This post has been edited 2 times. Last edited by vsamc, Apr 19, 2025, 2:51 AM
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