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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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[*]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
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
Divisibility NT
reni_wee   2
N a minute ago by reni_wee
Source: Iran 1998
Suppose that $a$ and $b$ are natural numbers such that
$$p = \frac{b}{4}\sqrt{\frac{2a-b}{2a+b}}$$is a prime number. Find all possible values of $a$,$b$,$p$.
2 replies
reni_wee
Today at 5:11 AM
reni_wee
a minute ago
Aslı tries to make the amount of stones at every unit square is equal
AlperenINAN   0
a minute ago
Source: Turkey JBMO TST P2
Let $n$ be a positive integer. Aslı and Zehra are playing a game on an $n\times n$ grid. Initially, $10n^2$ stones are placed on some of the unit squares of this grid.

On each move (starting with Aslı), Aslı chooses a row or a column that contains at least two squares with different numbers of stones, and Zehra redistributes the stones in that row or column so that after redistribution, the difference in the number of stones between any two squares in that row or column is at most one. Furthermore, this move must change the number of stones in at least one square.

For which values of $n$, regardless of the initial placement of the stones, can Aslı guarantee that every square ends up with the same number of stones?
0 replies
AlperenINAN
a minute ago
0 replies
Minimum value of a 3 variable expression
bin_sherlo   2
N 5 minutes ago by Tamam
Source: Türkiye 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.
2 replies
bin_sherlo
19 minutes ago
Tamam
5 minutes ago
ISI UGB 2025 P8
SomeonecoolLovesMaths   5
N 10 minutes ago by MathematicalArceus
Source: ISI UGB 2025 P8
Let $n \geq 2$ and let $a_1 \leq a_2 \leq \cdots \leq a_n$ be positive integers such that $\sum_{i=1}^{n} a_i = \prod_{i=1}^{n} a_i$. Prove that $\sum_{i=1}^{n} a_i \leq 2n$ and determine when equality holds.
5 replies
SomeonecoolLovesMaths
Today at 11:20 AM
MathematicalArceus
10 minutes ago
2n^2+4n-1 and 3n+4 have common powers
bin_sherlo   1
N 12 minutes ago by Burmf
Source: Türkiye 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 $3n+4$.
1 reply
bin_sherlo
22 minutes ago
Burmf
12 minutes ago
Trigo relation in a right angled. ISIBS2011P10
Sayan   9
N 12 minutes ago by sanyalarnab
Show that the triangle whose angles satisfy the equality
\[\frac{\sin^2A+\sin^2B+\sin^2C}{\cos^2A+\cos^2B+\cos^2C} = 2\]
is right angled.
9 replies
Sayan
Mar 31, 2013
sanyalarnab
12 minutes ago
Pentagon with given diameter, ratio desired
bin_sherlo   0
14 minutes ago
Source: Türkiye JBMO TST P7
$ABCDE$ is a pentagon whose vertices lie on circle $\omega$ where $\angle DAB=90^{\circ}$. Let $EB$ and $AC$ intersect at $F$, $EC$ meet $BD$ at $G$. $M$ is the midpoint of arc $AB$ on $\omega$, not containing $C$. If $FG\parallel DE\parallel CM$ holds, then what is the value of $\frac{|GE|}{|GD|}$?
0 replies
bin_sherlo
14 minutes ago
0 replies
Points on the sides of cyclic quadrilateral satisfy the angle conditions
AlperenINAN   0
20 minutes ago
Source: Turkey JBMO TST P1
Let $ABCD$ be a cyclic quadrilateral and let the intersection of $AB$ and $CD$ be $E$. Let the points $K,L$ be arbitrary points on sides $CD$ and $AB$ respectively which satisfy the conditions $\angle KAD=\angle KBC$ and $\angle LDA = \angle LCB$. Prove that $EK=EL$.
0 replies
AlperenINAN
20 minutes ago
0 replies
ISI UGB 2025 P2
SomeonecoolLovesMaths   4
N 33 minutes ago by MathsSolver007
Source: ISI UGB 2025 P2
If the interior angles of a triangle $ABC$ satisfy the equality, $$\sin ^2 A + \sin ^2 B + \sin^2  C = 2 \left( \cos ^2 A + \cos ^2 B + \cos ^2 C \right),$$prove that the triangle must have a right angle.
4 replies
SomeonecoolLovesMaths
Today at 11:16 AM
MathsSolver007
33 minutes ago
IMO ShortList 1998, combinatorics theory problem 5
orl   47
N 37 minutes ago by mathwiz_1207
Source: IMO ShortList 1998, combinatorics theory problem 5
In a contest, there are $m$ candidates and $n$ judges, where $n\geq 3$ is an odd integer. Each candidate is evaluated by each judge as either pass or fail. Suppose that each pair of judges agrees on at most $k$ candidates. Prove that \[{\frac{k}{m}} \geq {\frac{n-1}{2n}}. \]
47 replies
orl
Oct 22, 2004
mathwiz_1207
37 minutes ago
Cyclic equality implies equal sum of squares
blackbluecar   34
N 37 minutes ago by Markas
Source: 2021 Iberoamerican Mathematical Olympiad, P4
Let $a,b,c,x,y,z$ be real numbers such that

\[ a^2+x^2=b^2+y^2=c^2+z^2=(a+b)^2+(x+y)^2=(b+c)^2+(y+z)^2=(c+a)^2+(z+x)^2 \]
Show that $a^2+b^2+c^2=x^2+y^2+z^2$.
34 replies
blackbluecar
Oct 21, 2021
Markas
37 minutes ago
Common tangent to diameter circles
Stuttgarden   5
N 39 minutes ago by zuat.e
Source: Spain MO 2025 P2
The cyclic quadrilateral $ABCD$, inscribed in the circle $\Gamma$, satisfies $AB=BC$ and $CD=DA$, and $E$ is the intersection point of the diagonals $AC$ and $BD$. The circle with center $A$ and radius $AE$ intersects $\Gamma$ in two points $F$ and $G$. Prove that the line $FG$ is tangent to the circles with diameters $BE$ and $DE$.
5 replies
Stuttgarden
Mar 31, 2025
zuat.e
39 minutes ago
2020 EGMO P2: Sum inequality with permutations
alifenix-   29
N 40 minutes ago by Markas
Source: 2020 EGMO P2
Find all lists $(x_1, x_2, \ldots, x_{2020})$ of non-negative real numbers such that the following three conditions are all satisfied:

[list]
[*] $x_1 \le x_2 \le \ldots \le x_{2020}$;
[*] $x_{2020} \le x_1  + 1$;
[*] there is a permutation $(y_1, y_2, \ldots, y_{2020})$ of $(x_1, x_2, \ldots, x_{2020})$ such that $$\sum_{i = 1}^{2020} ((x_i + 1)(y_i + 1))^2 = 8 \sum_{i = 1}^{2020} x_i^3.$$[/list]

A permutation of a list is a list of the same length, with the same entries, but the entries are allowed to be in any order. For example, $(2, 1, 2)$ is a permutation of $(1, 2, 2)$, and they are both permutations of $(2, 2, 1)$. Note that any list is a permutation of itself.
29 replies
alifenix-
Apr 18, 2020
Markas
40 minutes ago
IMO 2018 Problem 2
juckter   97
N 42 minutes ago by Markas
Find all integers $n \geq 3$ for which there exist real numbers $a_1, a_2, \dots a_{n + 2}$ satisfying $a_{n + 1} = a_1$, $a_{n + 2} = a_2$ and
$$a_ia_{i + 1} + 1 = a_{i + 2},$$for $i = 1, 2, \dots, n$.

Proposed by Patrik Bak, Slovakia
97 replies
juckter
Jul 9, 2018
Markas
42 minutes ago
Soviet Union 2
orl   1
N Sep 5, 2004 by grobber
Source: IMO LongList 1959-1966 Problem 6
Let $m$ be a convex polygon in a plane, $l$ its perimeter and $S$ its area. Let $M\left( R\right) $ be the locus of all points in the space whose distance to $m$ is $\leq R,$ and $V\left(R\right) $ is the volume of the solid $M\left( R\right) .$


a.) Prove that \[V (R) = \frac 43 \pi R^3 +\frac{\pi}{2} lR^2 +2SR.\]

Hereby, we say that the distance of a point $C$ to a figure $m$ is $\leq R$ if there exists a point $D$ of the figure $m$ such that the distance $CD$ is $\leq R.$ (This point $D$ may lie on the boundary of the figure $m$ and inside the figure.)

additional question:

b.) Find the area of the planar $R$-neighborhood of a convex or non-convex polygon $m.$

c.) Find the volume of the $R$-neighborhood of a convex polyhedron, e. g. of a cube or of a tetrahedron.

Note by Darij: I guess that the ''$R$-neighborhood'' of a figure is defined as the locus of all points whose distance to the figure is $\leq R.$
1 reply
orl
Sep 1, 2004
grobber
Sep 5, 2004
Source: IMO LongList 1959-1966 Problem 6
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orl
3647 posts
#1 • 3 Y
Y by Adventure10, Adventure10, Mango247
Let $m$ be a convex polygon in a plane, $l$ its perimeter and $S$ its area. Let $M\left( R\right) $ be the locus of all points in the space whose distance to $m$ is $\leq R,$ and $V\left(R\right) $ is the volume of the solid $M\left( R\right) .$


a.) Prove that \[V (R) = \frac 43 \pi R^3 +\frac{\pi}{2} lR^2 +2SR.\]

Hereby, we say that the distance of a point $C$ to a figure $m$ is $\leq R$ if there exists a point $D$ of the figure $m$ such that the distance $CD$ is $\leq R.$ (This point $D$ may lie on the boundary of the figure $m$ and inside the figure.)

additional question:

b.) Find the area of the planar $R$-neighborhood of a convex or non-convex polygon $m.$

c.) Find the volume of the $R$-neighborhood of a convex polyhedron, e. g. of a cube or of a tetrahedron.

Note by Darij: I guess that the ''$R$-neighborhood'' of a figure is defined as the locus of all points whose distance to the figure is $\leq R.$
This post has been edited 2 times. Last edited by orl, Sep 2, 2004, 12:10 PM
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grobber
7849 posts
#2 • 2 Y
Y by Adventure10, Mango247
God! This is going to be awfully hard to explain in a rigorous manner, but I'll take a whack at it. :)

First of all, let's notice what $M(R)$ "looks like". If we place spheres of radius $R$ centered at each of the vertices of the polygon, then $M(R)$ is precisely the convex hull of the spheres. Alternatively, you may think that we place a sheet of rubber around the whole thing (polygon and spheres), and the set is what we obtain after the sheet has shrinked as much as possible.

a) In order to compute the volume, we need to compute the volume of three parts: the prism having the polygon as the median plane and having a height of $2R$ (this has volume $S\cdot R+S\cdot R=(2\cdot S)R$), the half-cylinders around the edges (this part has volume $\frac 12\sum a_i\cdot \pi R^2=(\frac \pi 2\cdot l)R^2$, where $a_i$ are the sides of the polygon), and whatever remains around the vertices. This last part is made up of sphere slices, which we can slide around on the sides of the polygon so that they form a sphere of radius $R$, so the volume is $(\frac 43\cdot \pi)R^3$.

b) The area is, again the sum of the areas of the three regions we have defined above: the area of the bases of the prism ($2S$), the areas of the half-cylinders, which is $l\cdot \pi R$, and the area of a sphere of radius $R$, which is $4\pi R^2$. The total area is thus $4\pi R^2+(\pi\cdot l)R+2\cdot S$.

c) Something similar to a). I'll be back later to edit this.
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