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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]
Our full course list for upcoming classes is below:
All classes run 7:30pm-8:45pm ET/4:30pm - 5:45pm PT unless otherwise noted.

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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
Irrational equation
giangtruong13   0
16 minutes ago
Solve the equation : $$(\sqrt{x}+1)[2-(x-6)\sqrt{x-3}]=x+8$$
0 replies
giangtruong13
16 minutes ago
0 replies
Classic graph theory lemma?
eulerleonhardfan   1
N 24 minutes ago by eulerleonhardfan
$n \in \mathbb{N}$ is given, $A$, $B$ are graphs on the same set of $n$ nodes, having $a, b$ connected components respectively. Prove that $A \cup B$ has at least $a+b-n$ connected components.
1 reply
eulerleonhardfan
30 minutes ago
eulerleonhardfan
24 minutes ago
circle geometry showing perpendicularity
Kyj9981   3
N 35 minutes ago by JollyEggsBanana
Two circles $\omega_1$ and $\omega_2$ intersect at points $A$ and $B$. A line through $B$ intersects $\omega_1$ and $\omega_2$ at points $C$ and $D$, respectively. Line $AD$ intersects $\omega_1$ at point $E \neq A$, and line $AC$ intersects $\omega_2$ at point $F \neq A$. If $O$ is the circumcenter of $\triangle AEF$, prove that $OB \perp CD$.
3 replies
Kyj9981
Mar 18, 2025
JollyEggsBanana
35 minutes ago
Min Number of Subsets of Strictly Increasing
taptya17   5
N 36 minutes ago by kotmhn
Source: India EGMO TST 2025 Day 1 P1
Let $n$ be a positive integer. Initially the sequence $0,0,\cdots,0$ ($n$ times) is written on the board. In each round, Ananya choses an integer $t$ and a subset of the numbers written on the board and adds $t$ to all of them. What is the minimum number of rounds in which Ananya can make the sequence on the board strictly increasing?

Proposed by Shantanu Nene
5 replies
taptya17
Dec 13, 2024
kotmhn
36 minutes ago
Nice inequality
sqing   3
N 43 minutes ago by Oksutok
Source: WYX
Let $a_1,a_2,\cdots,a_n  (n\ge 2)$ be real numbers . Prove that : There exist positive integer $k\in \{1,2,\cdots,n\}$ such that $$\sum_{i=1}^{n}\{kx_i\}(1-\{kx_i\})<\frac{n-1}{6}.$$Where $\{x\}=x-\left \lfloor x \right \rfloor.$
3 replies
sqing
Apr 24, 2019
Oksutok
43 minutes ago
Inspired by 2024 Fall LMT Guts
sqing   2
N an hour ago by Jackson0423
Source: Own
Let $x$, $y$, $z$ are pairwise distinct real numbers satisfying $x^2+y =y^2 +z = z^2+x. $ Prove that
$$(x+y)(y+z)(z+x)=-1$$Let $x$, $y$, $z$ are pairwise distinct real numbers satisfying $x^2+2y =y^2 +2z = z^2+2x. $ Prove that
$$(x+y)(y+z)(z+x)=-8$$
2 replies
sqing
2 hours ago
Jackson0423
an hour ago
Dividing Pairs
Jackson0423   2
N an hour ago by Jackson0423
Source: Own
Let \( a \) and \( b \) be positive integers.
Suppose that \( a \) is a divisor of \( b^2 + 1 \) and \( b \) is a divisor of \( a^2 + 1 \).
Find all such pairs \( (a, b) \).
2 replies
Jackson0423
Apr 13, 2025
Jackson0423
an hour ago
Ellipse and Vectors
scls140511   1
N an hour ago by Tigolf
Source: 2024 China Round 1 (Gao Lian)
7 Let $F_1$ and $F_2$ be the two foci of ellipse $\omega$. $P$ is a point on $\omega$. Let $O$ be the center of the excircle of $\triangle PF_1F_2$. When $\vec{PO} \cdot \vec{F_1F_2} = 2\vec{PF_1} \cdot \vec{PF_2}$, find the minimum eccentricity of $\omega$.
1 reply
scls140511
Sep 8, 2024
Tigolf
an hour ago
Maximum number of nice subsets
FireBreathers   1
N an hour ago by FireBreathers
Given a set $M$ of natural numbers with $n$ elements with $n$ odd number. A nonempty subset $S$ of $M$ is called $nice$ if the product of the elements of $S$ divisible by the sum of the elements of $M$, but not by its square. It is known that the set $M$ itself is good. Determine the maximum number of $nice$ subsets (including $M$ itself).
1 reply
FireBreathers
Yesterday at 10:27 PM
FireBreathers
an hour ago
Existence of reals satisfying cyclic relation
DVDthe1st   10
N an hour ago by sttsmet
Source: 2018 China TST Day 1 Q1
Let $p,q$ be positive reals with sum 1. Show that for any $n$-tuple of reals $(y_1,y_2,...,y_n)$, there exists an $n$-tuple of reals $(x_1,x_2,...,x_n)$ satisfying $$p\cdot \max\{x_i,x_{i+1}\} + q\cdot \min\{x_i,x_{i+1}\} = y_i$$for all $i=1,2,...,2017$, where $x_{2018}=x_1$.
10 replies
DVDthe1st
Jan 2, 2018
sttsmet
an hour ago
Inequalities from SXTX
sqing   13
N 2 hours ago by sqing
T702. Let $ a,b,c>0 $ and $ a+2b+3c=\sqrt{13}. $ Prove that $$ \sqrt{a^2+1} +2\sqrt{b^2+1} +3\sqrt{c^2+1} \geq 7$$S
T703. Let $ a,b $ be real numbers such that $ a+b\neq 0. $. Find the minimum of $ a^2+b^2+(\frac{1-ab}{a+b} )^2.$
T704. Let $ a,b,c>0 $ and $ a+b+c=3. $ Prove that $$ \frac{a^2+7}{(c+a)(a+b)} + \frac{b^2+7}{(a+b)(b+c)} +\frac{c^2+7}{(b+c)(c+a)}  \geq 6$$S
13 replies
sqing
Feb 18, 2025
sqing
2 hours ago
Combinatorics problem
lgx57   1
N 4 hours ago by alexheinis
There are $100$ positive integer arrays $\{a_{1,n}\},\{a_{2,n}\},\cdots,\{a_{100,n}\}$, and they are all infinity arrays.
Prove that: There exists $ m<k$, that for every integer $1 \le i \le 100, a_{i,m}<a_{i,k}$
1 reply
lgx57
Apr 14, 2025
alexheinis
4 hours ago
Span to the infinity??
dotscom26   1
N 4 hours ago by P0tat0b0y
The equation \[
\sqrt[3]{\sqrt[3]{x - \frac{3}{8}} - \frac{3}{8}} = x^3 + \frac{3}{8}
\]has exactly two real positive solutions \( r \) and \( s \). Compute \( r + s \).
1 reply
dotscom26
4 hours ago
P0tat0b0y
4 hours ago
Inequalities
sqing   19
N 6 hours ago by sqing
Let $ a,b,c> 0 $ and $ ab+bc+ca\leq  3abc . $ Prove that
$$ a+ b^2+c\leq a^2+ b^3+c^2 $$$$ a+ b^{11}+c\leq a^2+ b^{12}+c^2 $$
19 replies
sqing
Apr 22, 2025
sqing
6 hours ago
volume of pyramid wanted (2010 Euler Teachers' MO I p9)
parmenides51   2
N Jul 20, 2020 by duck_master
The side edges $PA, PB, PC$ of the pyramid $PABC$ are equal to $2, 2$, and $3$, respectively the base of the ABC is a regular triangle. It is known that the area of the lateral faces of the pyramid are equal to each other. Find the volume of the pyramid $PABC$ .
2 replies
parmenides51
Jul 10, 2020
duck_master
Jul 20, 2020
volume of pyramid wanted (2010 Euler Teachers' MO I p9)
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parmenides51
30630 posts
#1 • 1 Y
Y by Mango247
The side edges $PA, PB, PC$ of the pyramid $PABC$ are equal to $2, 2$, and $3$, respectively the base of the ABC is a regular triangle. It is known that the area of the lateral faces of the pyramid are equal to each other. Find the volume of the pyramid $PABC$ .
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vanstraelen
8985 posts
#2 • 1 Y
Y by Vin0997
The Russian answer says: this pyramid does not exist.
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duck_master
1719 posts
#3 • 2 Y
Y by Mango247, Mango247
Elaborating on the previous poster's answer
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N Quick Reply
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