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k a April Highlights and 2025 AoPS Online Class Information
jlacosta   0
Apr 2, 2025
Spring is in full swing and summer is right around the corner, what are your plans? At AoPS Online our schedule has new classes starting now through July, so be sure to keep your skills sharp and be prepared for the Fall school year! Check out the schedule of upcoming classes below.

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Looking for summer camps in math and language arts? Be sure to check out the video-based summer camps offered at the Virtual Campus that are 2- to 4-weeks in duration. 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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April 9th (Webinar), 4:00pm PT/7:00pm ET, Learn about Video-based Summer Camps at the Virtual Campus
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[*]April 22nd (Webinar), 4:00pm PT/7:00pm ET, Competitive Programming at AoPS (USACO).[/list]
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0 replies
jlacosta
Apr 2, 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
IMO ShortList 2002, number theory problem 1
orl   77
N 4 minutes ago by Ilikeminecraft
Source: IMO ShortList 2002, number theory problem 1
What is the smallest positive integer $t$ such that there exist integers $x_1,x_2,\ldots,x_t$ with \[x^3_1+x^3_2+\,\ldots\,+x^3_t=2002^{2002}\,?\]
77 replies
orl
Sep 28, 2004
Ilikeminecraft
4 minutes ago
(m^2+n)(m+n^2)=(m-n)^3
Binomial-theorem   29
N 5 minutes ago by Ilikeminecraft
Source: USAMO 1987 problem 1
Determine all solutions in non-zero integers $a$ and $b$ of the equation \[(a^2+b)(a+b^2) = (a-b)^3.\]
29 replies
Binomial-theorem
Jul 24, 2011
Ilikeminecraft
5 minutes ago
Config geo with symmedian
a_507_bc   6
N 29 minutes ago by ihategeo_1969
Source: Serbia Additional IMO TST 2024, P3 (out of 4)
Let $ABC$ be a triangle with circumcenter $O$, angle bisector $AD$ with $D \in BC$ and altitude $AE$ with $E \in BC$. The lines $AO$ and $BC$ meet at $I$. The circumcircle of $\triangle ADE$ meets $AB, AC$ at $F, G$ and $FG$ meets $BC$ at $H$. The circumcircles of triangles $AHI$ and $ABC$ meet at $J$. Show that $AJ$ is a symmedian in $\triangle ABC$
6 replies
a_507_bc
May 30, 2024
ihategeo_1969
29 minutes ago
Prove that the number of $a$ is o(p)
Seungjun_Lee   13
N an hour ago by ihategeo_1969
Source: 2024 FKMO P6
Prove that there exists a positive integer $K$ that satisfies the following condition.

Condition: For any prime $p > K$, the number of positive integers $a \le p$ that $p^2 \mid a^{p-1} - 1$ is less than $\frac{p}{2^{2024}}$
13 replies
Seungjun_Lee
Mar 24, 2024
ihategeo_1969
an hour ago
Congruence related perimeter
egxa   4
N an hour ago by Geometrineq
Source: All Russian 2025 9.8 and 10.8
On the sides of triangle \( ABC \), points \( D_1, D_2, E_1, E_2, F_1, F_2 \) are chosen such that when going around the triangle, the points occur in the order \( A, F_1, F_2, B, D_1, D_2, C, E_1, E_2 \). It is given that
\[
AD_1 = AD_2 = BE_1 = BE_2 = CF_1 = CF_2.
\]Prove that the perimeters of the triangles formed by the lines \( AD_1, BE_1, CF_1 \) and \( AD_2, BE_2, CF_2 \) are equal.
4 replies
egxa
Apr 18, 2025
Geometrineq
an hour ago
Killer NT that nobody solved (also my hardest NT ever created)
mshtand1   8
N an hour ago by mshtand1
Source: Ukraine IMO 2025 TST P8
A positive integer number \( a \) is chosen. Prove that there exists a prime number that divides infinitely many terms of the sequence \( \{b_k\}_{k=1}^{\infty} \), where
\[
b_k = a^{k^k} \cdot 2^{2^k - k} + 1.
\]
Proposed by Arsenii Nikolaev and Mykhailo Shtandenko
8 replies
mshtand1
Apr 19, 2025
mshtand1
an hour ago
Value of the sum
fermion13pi   1
N 2 hours ago by RagvaloD
Source: Australia
Calculate the value of the sum

\sum_{k=1}^{9999999} \frac{1}{(k+1)^{3/2} + (k^2-1)^{1/3} + (k-1)^{2/3}}.
1 reply
fermion13pi
5 hours ago
RagvaloD
2 hours ago
Octagon Problem
Shiyul   10
N 2 hours ago by mathprodigy2011
The vertices of octagon $ABCDEFGH$ lie on the same circle. If $AB = BC = CD = DE = 11$ and $EF = FG = GH = HA = \sqrt2$, what is the area of octagon $ABCDEFGH$?

I approached this problem by noticing that the area of the octagon is the area of the eight isoceles triangles with lengths $r$, $r$, and $sqrt2$ or 11. However, I didn't know how to find the radius. Can anyone give me a hint?
10 replies
Shiyul
Yesterday at 11:41 PM
mathprodigy2011
2 hours ago
Quad formed by orthocenters has same area (all 7's!)
v_Enhance   37
N 3 hours ago by lpieleanu
Source: USA January TST for the 55th IMO 2014
Let $ABCD$ be a cyclic quadrilateral, and let $E$, $F$, $G$, and $H$ be the midpoints of $AB$, $BC$, $CD$, and $DA$ respectively. Let $W$, $X$, $Y$ and $Z$ be the orthocenters of triangles $AHE$, $BEF$, $CFG$ and $DGH$, respectively. Prove that the quadrilaterals $ABCD$ and $WXYZ$ have the same area.
37 replies
v_Enhance
Apr 28, 2014
lpieleanu
3 hours ago
USAMO 2002 Problem 3
MithsApprentice   20
N 4 hours ago by Mathandski
Prove that any monic polynomial (a polynomial with leading coefficient 1) of degree $n$ with real coefficients is the average of two monic polynomials of degree $n$ with $n$ real roots.
20 replies
MithsApprentice
Sep 30, 2005
Mathandski
4 hours ago
NT equations make a huge comeback
MS_Kekas   3
N 4 hours ago by RagvaloD
Source: Ukrainian Mathematical Olympiad 2024. Day 1, Problem 11.1
Find all pairs $a, b$ of positive integers, for which

$$(a, b) + 3[a, b] = a^3 - b^3$$
Here $(a, b)$ denotes the greatest common divisor of $a, b$, and $[a, b]$ denotes the least common multiple of $a, b$.

Proposed by Oleksiy Masalitin
3 replies
1 viewing
MS_Kekas
Mar 19, 2024
RagvaloD
4 hours ago
FSJM Semi Final 2025; Problem 12: Square and Trapezoids
Themathwhiz524   1
N 4 hours ago by vanstraelen


On the extension of [AB] , one of the sides of a square ABCD with a side length of 74 cm, a point M is placed such that BM = 13 cm. A line is drawn from M that divides the square into two trapezoids of equal area. This line intersects [BC] at point E .


What is the exact length of BE in cm?
Round to the nearest hundredth if necessary.
1 reply
Themathwhiz524
Mar 15, 2025
vanstraelen
4 hours ago
Newton's Sum
P162008   7
N 5 hours ago by vanstraelen
If $\sum_{cyc} a = 7, \sum_{cyc} a^2 = 15, \sum_{cyc} a^3 = 19$ and $\sum_{cyc} a^4 = 25$ where each summation runs over $4$ variables $a,b,c$ and $d.$ Then find the value of $\sum_{cyc} a^5.$
7 replies
P162008
Today at 1:51 AM
vanstraelen
5 hours ago
geometry question
kjhgyuio   4
N Today at 5:54 PM by undefined-NaN
________
4 replies
kjhgyuio
Apr 8, 2025
undefined-NaN
Today at 5:54 PM
right triangles. same perimeter & area (2016 Kurchatov Olympiad 11 p1 - Russia)
parmenides51   13
N Feb 15, 2023 by Richie
Two right-angled triangles have the same area and perimeter. Is it obligatory are these triangles congruent?
13 replies
parmenides51
Mar 8, 2021
Richie
Feb 15, 2023
right triangles. same perimeter & area (2016 Kurchatov Olympiad 11 p1 - Russia)
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parmenides51
30632 posts
#1 • 2 Y
Y by son7, ImSh95
Two right-angled triangles have the same area and perimeter. Is it obligatory are these triangles congruent?
This post has been edited 1 time. Last edited by parmenides51, Mar 8, 2021, 3:56 PM
Reason: replaced equal with congruent to be more specific
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eduD_looC
6610 posts
#2 • 1 Y
Y by ImSh95
No. I remember there was an AMC 12 question that kinda disproved this.

oops this is right triangles nvm
This post has been edited 1 time. Last edited by eduD_looC, Mar 8, 2021, 3:55 PM
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themathboi101
913 posts
#3 • 1 Y
Y by ImSh95
What do you mean by “equal”
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parmenides51
30632 posts
#4 • 2 Y
Y by themathboi101, ImSh95
equal triangles means congruent ones
This post has been edited 2 times. Last edited by parmenides51, Mar 8, 2021, 3:55 PM
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HamstPan38825
8857 posts
#5 • 1 Y
Y by ImSh95
According to WA I'm not getting anything that looks like a good counterexample.
Attachments:
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ezpotd
1260 posts
#6 • 1 Y
Y by ImSh95
Consider two right triangles with area $\frac{1}{2}$, since scaling up area by some amount will scale perimeter by the square root of that amount, if the perimeters are unequal, they will still be unequal after a scale. Then the perimeter of a triangle that has side length $x \leq 1$ is $x + \frac{1}{x} + \sqrt{x^2+\frac{1}{x^2}}$. If we can prove that the derivative is positive or negative for the entire interval $0,1$, we will be done.

$1 - \frac{1}{x^2} + \frac{x - \frac{1}{x^3}}{\sqrt{x^2 + \frac{1}{x^2}}}$. We can now just prove $1 \leq \frac{1}{x^2}, x \leq \frac{1}{x^3}$, both of which are trivial given $x \leq 1$. Therefore, there exists no noncongruent right triangles with the same area and perimeter.
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sotpidot
290 posts
#7 • 2 Y
Y by ImSh95, Mango247
Since the area of a right triangle is directly correlated to the lengths of its legs, this is the same as saying:

If $a + b = c + d$ and $ab = cd$ with $a \leq b$ and $c \leq d$, then $a=c$ and $b=d$.

This is obviously true (simple algebra if you want to be rigorous), so the triangles are congruent.

Edit: sniped again rip
This post has been edited 1 time. Last edited by sotpidot, Mar 8, 2021, 4:36 PM
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parmenides51
30632 posts
#8 • 2 Y
Y by HWenslawski, ImSh95
@above, your idea takes for granted that they have the same hypotenuse which is not given (at all cases)
This post has been edited 1 time. Last edited by parmenides51, Mar 8, 2021, 5:26 PM
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10000th User
3049 posts
#9 • 17 Y
Y by samrocksnature, jhu08, gnidoc, megarnie, fuzimiao2013, centslordm, mod_x, ObjectZ, pog, HWenslawski, ImSh95, rg_ryse, ultimate_life_form, aidan0626, Mango247, Spiritpalm, Luckydragon21
The perimeter equation should be $a+b+\sqrt{a^2+b^2}=c+d+\sqrt{c^2+d^2}$.
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AKS_9_54_61
332 posts
#10 • 2 Y
Y by HWenslawski, ImSh95
So I assumed two right triangles with hypotenuses $a,b$ and one angle $x,y$ and simplified using those conditions and got this equation

$\cos(0.5 (x - y)) (\cos(x) + \sin(x) - \cos(y) - \sin(y)) + \cos(0.5 (x + y)) (\sin(x) + \cos(y) - \sin(y) - \cos(x)) = 0$

Now Geoegbra suggests, it does have non-trivial solutions idk
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donian9265
541 posts
#12 • 3 Y
Y by megarnie, HWenslawski, ImSh95
I don't see anything wrong with this solution which I think is rigorous and fairly straight forward but maybe somebody else can point out a flaw.
solution
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Blahblah009
296 posts
#13 • 1 Y
Y by ImSh95
$$                      $$
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isache
439 posts
#14
Y by
This is easy, take the 5-12-13 and 6-8-10 triangles.
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Richie
1598 posts
#15
Y by
parmenides51 wrote:
Two right-angled triangles have the same area and perimeter. Is it obligatory are these triangles congruent?

We know in-radius $r=\frac{\triangle}{s}$.
Since both the right angled triangles have same area and perimeter we can say the in-radii are equal too.
We know that the in-radius of a right angled triangle is $\frac{l+b-h}{2}$, where $h$ is the hypotenuse.
Let the two legs and the hypotenuse of the two triangles be $a,b,c$ and $x,y,z$ respectively where $c$ and $z$ are the hypotenuses.
We have perimeter equal, so $a+b+c=x+y+z$ ----(i)
Again in-radii are equal, so $a+b-c=x+y-z$-----(ii)
And finally areas are equal, so $ab=xy$ ----(iii)
Doing equation (i)-(ii), we get $2c=2z$, which implies $c=z$
Since $c=z$ and perimeters are same, we get $a+b=x+y$
As the hypotenuses are equal we have $a^2+b^2=x^2+y^2$
And being area same we already know $ab=xy$
So we have $a^2+b^2-2ab=x^2+y^2-2xy$
Hence $(a-b)^2=(x-y)^2$. This implies $a-b=x-y$. Assuming $a>b$ and $x>y$
We have $a+b=x+y$ and $a-b=x-y$. Adding and subtracting these two we get $a=x$ and $b=y$.
Game over. :thumbup:
This post has been edited 1 time. Last edited by Richie, Feb 15, 2023, 12:56 PM
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