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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.

WOOT early bird pricing is in effect, don’t miss out! If you took MathWOOT Level 2 last year, no worries, it is all new problems this year! Our Worldwide Online Olympiad Training program is for high school level competitors. AoPS designed these courses to help our top students get the deep focus they need to succeed in their specific competition goals. Check out the details at this link for all our WOOT programs in math, computer science, chemistry, and physics.

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)!

Be sure to mark your calendars for the following events:
[list][*]April 3rd (Webinar), 4pm PT/7:00pm ET, Learning with AoPS: Perspectives from a Parent, Math Camp Instructor, and University Professor
[*]April 8th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MATHCOUNTS State Discussion
April 9th (Webinar), 4:00pm PT/7:00pm ET, Learn about Video-based Summer Camps at the Virtual Campus
[*]April 10th (Math Jam), 4:30pm PT/7:30pm ET, 2025 MathILy and MathILy-Er Math Jam: Multibackwards Numbers
[*]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
Website to learn math
hawa   34
N 13 minutes ago by iwastedmyusername
Hi, I'm kinda curious what website do yall use to learn math, like i dont find any website thats fun to learn math
34 replies
hawa
Apr 9, 2025
iwastedmyusername
13 minutes ago
2500th post
Solocraftsolo   19
N 29 minutes ago by b2025tyx
i keep forgetting to do these...


2500 is cool.

i am not very sentimental so im not going to post a math story or anything.

here are some problems though

p1p2p3

p4
19 replies
Solocraftsolo
Apr 16, 2025
b2025tyx
29 minutes ago
Bogus Proof Marathon
pifinity   7583
N 33 minutes ago by HM2018
Hi!
I'd like to introduce the Bogus Proof Marathon.

In this marathon, simply post a bogus proof that is middle-school level and the next person will find the error. You don't have to post the real solution :P

Use classic Marathon format:
[hide=P#]a1b2c3[/hide]
[hide=S#]a1b2c3[/hide]


Example posts:

P(x)
-----
S(x)
P(x+1)
-----
Let's go!! Just don't make it too hard!
7583 replies
pifinity
Mar 12, 2018
HM2018
33 minutes ago
Combinatorics
TUAN2k8   1
N 33 minutes ago by TUAN2k8
A sequence of integers $a_1,a_2,...,a_k$ is call $k-balanced$ if it satisfies the following properties:
$i) a_i \neq a_j$ and $a_i+a_j \neq 0$ for all indices $i \neq j$.
$ii) \sum_{i=1}^{k} a_i=0$.
Find the smallest integer $k$ for which: Every $k-balanced$ sequence, there always exist two terms whose diffence is not less than $n$. (where $n$ is given positive integer)
1 reply
TUAN2k8
Today at 8:22 AM
TUAN2k8
33 minutes ago
Euler line of incircle touching points /Reposted/
Eagle116   3
N 39 minutes ago by Eagle116
Let $ABC$ be a triangle with incentre $I$ and circumcentre $O$. Let $D,E,F$ be the touchpoints of the incircle with $BC$, $CA$, $AB$ respectively. Prove that $OI$ is the Euler line of $\vartriangle DEF$.
3 replies
Eagle116
2 hours ago
Eagle116
39 minutes ago
IMO Shortlist 2012, Number Theory 1
lyukhson   44
N 40 minutes ago by g0USinsane777
Source: IMO Shortlist 2012, Number Theory 1
Call admissible a set $A$ of integers that has the following property:
If $x,y \in A$ (possibly $x=y$) then $x^2+kxy+y^2 \in A$ for every integer $k$.
Determine all pairs $m,n$ of nonzero integers such that the only admissible set containing both $m$ and $n$ is the set of all integers.

Proposed by Warut Suksompong, Thailand
44 replies
lyukhson
Jul 29, 2013
g0USinsane777
40 minutes ago
Easy Geometry
Itoz   2
N 44 minutes ago by Lil_flip38
Source: Own
$\triangle ABC$ satisfies $AC>BC$, and its incenter is $I$. $D$ is the foot from $I$ to $AC$and $E$ is a point on segment $AC$ such that $BC=CE$. Line $BD$ meets $\odot (BCE)$ at point $F(\ne B)$, and the orthocenter of $\triangle AEI$ is $H$.

Prove that $\odot(AEH)$ is tangent to $\odot(CDF)$.
2 replies
Itoz
3 hours ago
Lil_flip38
44 minutes ago
Common chord bisects segment
mofumofu   11
N an hour ago by sttsmet
Source: China TSTST 3 Day 1 Q2
Let $ABCD$ be a non-cyclic convex quadrilateral. The feet of perpendiculars from $A$ to $BC,BD,CD$ are $P,Q,R$ respectively, where $P,Q$ lie on segments $BC,BD$ and $R$ lies on $CD$ extended. The feet of perpendiculars from $D$ to $AC,BC,AB$ are $X,Y,Z$ respectively, where $X,Y$ lie on segments $AC,BC$ and $Z$ lies on $BA$ extended. Let the orthocenter of $\triangle ABD$ be $H$. Prove that the common chord of circumcircles of $\triangle PQR$ and $\triangle XYZ$ bisects $BH$.
11 replies
mofumofu
Mar 18, 2017
sttsmet
an hour ago
MONT pg 31 example 1.10.40
Jaxman8   1
N an hour ago by hanulyeongsam
Can somebody explain why it works.
1 reply
Jaxman8
Thursday at 9:33 PM
hanulyeongsam
an hour ago
Interesting F.E
Jackson0423   4
N an hour ago by Jackson0423
Show that there does not exist a function
\[
f : \mathbb{R}^+ \to \mathbb{R}
\]satisfying the condition that for all \( x, y \in \mathbb{R}^+ \),
\[
f(x^2 + y) \geq f(x) + y.
\]

~Korea 2017 P7
4 replies
Jackson0423
Yesterday at 4:12 PM
Jackson0423
an hour ago
Reflections of AB, AC with respect to BC and angle bisector of A
falantrng   27
N an hour ago by ravengsd
Source: BMO 2024 Problem 1
Let $ABC$ be an acute-angled triangle with $AC > AB$ and let $D$ be the foot of the
$A$-angle bisector on $BC$. The reflections of lines $AB$ and $AC$ in line $BC$ meet $AC$ and $AB$ at points
$E$ and $F$ respectively. A line through $D$ meets $AC$ and $AB$ at $G$ and $H$ respectively such that $G$
lies strictly between $A$ and $C$ while $H$ lies strictly between $B$ and $F$. Prove that the circumcircles of
$\triangle EDG$ and $\triangle FDH$ are tangent to each other.
27 replies
falantrng
Apr 29, 2024
ravengsd
an hour ago
Test from Côte d'Ivoire Diophantine equation
MENELAUSS   0
an hour ago
determine all triplets $(x;y;z)$ of natural numbers such that
$$y  \quad  \text{is prime }$$
$$y \quad \text{and} \quad 3  \quad \text{does not divide} \quad z$$
$$x^3-y^3=z^2$$
0 replies
MENELAUSS
an hour ago
0 replies
Geometry Transformation Problems
ReticulatedPython   4
N an hour ago by cheltstudent
Problem 1:
A regular hexagon of side length $1$ is rotated $360$ degrees about one side. The space through which the hexagon travels forms a solid. Find the volume of this solid.

Problem 2:

A regular octagon of side length $1$ is rotated $360$ degrees about one side. The space through which the octagon travels through forms a solid. Find the volume of this solid.

Source:Own

Hint

Useful Formulas
4 replies
ReticulatedPython
Apr 17, 2025
cheltstudent
an hour ago
Substitutions inequality?
giangtruong13   2
N an hour ago by giangtruong13
Let $a,b,c>0$ such that: $a^2b^2+ c^2b^2+ a^2c^2=3(abc)^2$. Prove that: $$\sum \frac{b+c}{a} \geq 2\sqrt{3(ab+bc+ca)}$$
2 replies
giangtruong13
Yesterday at 2:07 PM
giangtruong13
an hour ago
Annoying Probability Math Problem
RYang2   13
N Yesterday at 2:00 AM by FabulousSpider24
I was working in my math textbook(not the AoPS one) when I came across this math problem:

Determine if the events are dependent or independent.
1. Drawing a red and a blue marble at the same time from a bag containing 6 red and 4 blue marbles
2.(omitted)

I thought it was independent, since the events happen at the same time, but the textbook answer said dependent.
Can someone help me understand(or prove the textbook wrong)?
13 replies
RYang2
Mar 14, 2018
FabulousSpider24
Yesterday at 2:00 AM
Annoying Probability Math Problem
G H J
G H BBookmark kLocked kLocked NReply
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RYang2
1936 posts
#1 • 2 Y
Y by Adventure10, Mango247
I was working in my math textbook(not the AoPS one) when I came across this math problem:

Determine if the events are dependent or independent.
1. Drawing a red and a blue marble at the same time from a bag containing 6 red and 4 blue marbles
2.(omitted)

I thought it was independent, since the events happen at the same time, but the textbook answer said dependent.
Can someone help me understand(or prove the textbook wrong)?
This post has been edited 1 time. Last edited by RYang2, Mar 14, 2018, 5:10 PM
Reason: Too general subject
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math_is_life_2004
1397 posts
#2 • 1 Y
Y by Adventure10
It’s dependent
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RYang2
1936 posts
#3 • 1 Y
Y by Adventure10
Explain?
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math_is_life_2004
1397 posts
#4 • 2 Y
Y by Adventure10, Mango247
Actually I think its independent what grade textbook you have?
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brainpopper
1052 posts
#5 • 2 Y
Y by Adventure10, Mango247
Independent is only when they are replace or when the probability doesn't change, right? In #1, If we draw a blue marble first, the probability is 6/10 but the next red marble is 4/9
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RYang2
1936 posts
#6 • 2 Y
Y by Adventure10, Mango247
Pre-Algebra Textbook
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RYang2
1936 posts
#7 • 2 Y
Y by Adventure10, Mango247
And, the problem said at the same time, so there would be no "first" or "second"
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math_is_life_2004
1397 posts
#8 • 2 Y
Y by Adventure10, Mango247
RYang2 wrote:
Pre-Algebra Textbook

Oh I haven’t done that for 2 years. After you memorized the law of cosine you kinda forget everything. #2ndquadraticequation
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creeperhissboom
224 posts
#9 • 2 Y
Y by Adventure10, Mango247
It is dependant.

It is the same as taking one out at a time.
It is only independant if there is replacement.
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A-Username
70 posts
#10 • 2 Y
Y by Adventure10, Mango247
RYang2 wrote:
I was working in my math textbook(not the AoPS one) when I came across this math problem:

Determine if the events are dependent or independent.
1. Drawing a red and a blue marble at the same time from a bag containing 6 red and 4 blue marbles
2.(omitted)

I thought it was independent, since the events happen at the same time, but the textbook answer said dependent.
Can someone help me understand(or prove the textbook wrong)?

@RYang2 Easy explanation for #1 is
Independent-Event 1 doesn't influence Event 2.
Dependent-Event 1 does influence Event 2.
Since this bag contains 6 red and 4 blues, there are 10 marbles in the bag. Now, we know that the color doesn't really matter because we know there is more than 1 for each color. Then we can determine which definition it fits better. First, we know it can't be dependent because if we take it at the same time, there is no sense of order and that the taking of the blue doesn't affect the number of reds there are and vice versa.
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EthanNg6
13 posts
#11
Y by
It's probably dependent
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Jaxman8
113 posts
#12
Y by
I think dependent, if you were to calculate the probabilities for blue first vs red first it’s the same
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giratina3
494 posts
#13 • 1 Y
Y by EthanNg6
The answer is dependent. When you pick 2 marbles, the first pick affects the second one. Although you pick the two at the same time, the change in marble just occurs instantly, so it is still dependent (most average school textbook problem)
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FabulousSpider24
66 posts
#14 • 1 Y
Y by EthanNg6
You can think about it like this: It is dependent because as soon as the first marble is taken, the number of marbles in the bag decreases and so the probability of picking a marble (either red or blue) will change immediately afterwards. .
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