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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
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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
Solllllllvvve
youochange   3
N 17 minutes ago by sadat465
Source: All Russian Olympiad 2017 Day 1 grade 10 P5
Suppose n is a composite positive integer. Let $1 = a_1 < a_2 < · · · < a_k = n$ be all the divisors of $n$. It is known, that $a_1+1, . . . , a_k+1$ are all divisors for some $m $(except $1, m$). Find all such $n.$
3 replies
youochange
Jan 12, 2025
sadat465
17 minutes ago
a_n >= 1/n if a_{n+1}^2 + a_{n+1} = a_n, a_1=1 , a_i>=0
parmenides51   13
N 30 minutes ago by Safal
Source: Canadian Junior Mathematical Olympiad - CJMO 2020 p1
Let $a_1, a_2, a_3, . . .$ be a sequence of positive real numbers that satisfies $a_1 = 1$ and $a^2_{n+1} + a_{n+1} = a_n$ for every natural number $n$. Prove that $a_n  \ge \frac{1}{n}$ for every natural number $n$.
13 replies
parmenides51
Jul 15, 2020
Safal
30 minutes ago
Inspired by giangtruong13
sqing   4
N 42 minutes ago by kokcio
Source: Own
Let $ a,b,c,d\geq 0 ,a-b+d=21 $ and $ a+3b+4c=101 $. Prove that
$$ 61\leq  a+b+2c+d\leq \frac{265}{3}$$$$- \frac{2121}{2}\leq   ab+bc-2cd+da\leq \frac{14045}{12}$$$$\frac{519506-7471\sqrt{7471}}{27}\leq   ab+bc-2cd+3da\leq 33620$$
4 replies
sqing
Yesterday at 2:57 AM
kokcio
42 minutes ago
Number Theory Chain!
JetFire008   33
N an hour ago by Primeniyazidayi
I will post a question and someone has to answer it. Then they have to post a question and someone else will answer it and so on. We can only post questions related to Number Theory and each problem should be more difficult than the previous. Let's start!

Question 1
33 replies
JetFire008
Apr 7, 2025
Primeniyazidayi
an hour ago
Inequality with a,b,c
GeoMorocco   1
N an hour ago by Natrium
Source: Morocco Training
Let $   a,b,c   $ be positive real numbers such that : $   ab+bc+ca=3   $ . Prove that : $$\frac{\sqrt{1+a^2}}{1+ab}+\frac{\sqrt{1+b^2}}{1+bc}+\frac{\sqrt{1+c^2}}{1+ca}\ge \sqrt{\frac{3(a+b+c)}{2}}$$
1 reply
GeoMorocco
Yesterday at 10:05 PM
Natrium
an hour ago
IMO Shortlist 2013, Number Theory #1
lyukhson   149
N an hour ago by SSS_123
Source: IMO Shortlist 2013, Number Theory #1
Let $\mathbb{Z} _{>0}$ be the set of positive integers. Find all functions $f: \mathbb{Z} _{>0}\rightarrow \mathbb{Z} _{>0}$ such that
\[ m^2 + f(n) \mid mf(m) +n \]
for all positive integers $m$ and $n$.
149 replies
lyukhson
Jul 10, 2014
SSS_123
an hour ago
Tangents and chord
iv999xyz   1
N 2 hours ago by aidenkim119
Given a circle with chord AB. k and l are tangents to the circle at points A and B. C and E are in different half-planes with respect to AB and lie on k, and F and D are in different half-planes with respect to AB and lie on l. Furthermore, C and F are in the same half-plane with respect to AB and AC = BD; AE = BF. CD intersects the circle at P and R and EF intersects the circle at Q and S. P and Q are in the same half-plane with respect to AB and in different half-plane with R and S. Prove that PQRS is a parallelogram if and only if AB, CD, and EF intersect at one point.
1 reply
iv999xyz
Today at 9:41 AM
aidenkim119
2 hours ago
Find the area enclosed by the curve |z|^2 + |z^2 - 2i| = 16
mqoi_KOLA   2
N 2 hours ago by mqoi_KOLA
Find the area of the Argand plane enclosed by the curve $$ |z|^2 + |z^2 - 2i| = 16.$$(ans- $3 \sqrt7 \pi$)
2 replies
mqoi_KOLA
Today at 11:58 AM
mqoi_KOLA
2 hours ago
Very tight inequalities
KhuongTrang   2
N 3 hours ago by SunnyEvan
Source: own
Problem. Given non-negative real numbers $a,b,c$ satisfying $ab+bc+ca=1.$ Prove that $$\color{black}{\frac{1}{35a+12b+2}+\frac{1}{35b+12c+2}+\frac{1}{35c+12a+2}\ge \frac{4}{39}.}$$$$\color{black}{\frac{1}{4a+9b+6}+\frac{1}{4b+9c+6}+\frac{1}{4c+9a+6}\le \frac{2}{9}.}$$When does equality hold?
2 replies
KhuongTrang
May 17, 2024
SunnyEvan
3 hours ago
Sum of First, Second, and Third Powers
Brut3Forc3   47
N 3 hours ago by cubres
Source: 1973 USAMO Problem 4
Determine all roots, real or complex, of the system of simultaneous equations
\begin{align*} x+y+z &= 3, \\
x^2+y^2+z^2 &= 3, \\
x^3+y^3+z^3 &= 3.\end{align*}
47 replies
Brut3Forc3
Mar 7, 2010
cubres
3 hours ago
Indonesia Regional MO 2019 Part A
parmenides51   13
N 3 hours ago by SomeonecoolLovesMaths
Indonesia Regional MO
Year 2019 Part A

Time: 90 minutes Rules


p1. In the bag there are $7$ red balls and $8$ white balls. Audi took two balls at once from inside the bag. The chance of taking two balls of the same color is ...


p2. Given a regular hexagon with a side length of $1$ unit. The area of the hexagon is ...


p3. It is known that $r, s$ and $1$ are the roots of the cubic equation $x^3 - 2x + c = 0$. The value of $(r-s)^2$ is ...


p4. The number of pairs of natural numbers $(m, n)$ so that $GCD(n,m) = 2$ and $LCM(m,n) = 1000$ is ...


p5. A data with four real numbers $2n-4$, $2n-6$, $n^2-8$, $3n^2-6$ has an average of $0$ and a median of $9/2$. The largest number of such data is ...


p6. Suppose $a, b, c, d$ are integers greater than $2019$ which are four consecutive quarters of an arithmetic row with $a <b <c <d$. If $a$ and $d$ are squares of two consecutive natural numbers, then the smallest value of $c-b$ is ...


p7. Given a triangle $ABC$, with $AB = 6$, $AC = 8$ and $BC = 10$. The points $D$ and $E$ lies on the line segment $BC$. with $BD = 2$ and $CE = 4$. The measure of the angle $\angle DAE$ is ...


p8. Sequqnce of real numbers $a_1,a_2,a_3,...$ meet $\frac{na_1+(n-1)a_2+...+2a_{n-1}+a_n}{n^2}=1$ for each natural number $n$. The value of $a_1a_2a_3...a_{2019}$ is ....


p9. The number of ways to select four numbers from $\{1,2,3, ..., 15\}$ provided that the difference of any two numbers at least $3$ is ...


p10. Pairs of natural numbers $(m , n)$ which satisfies $$m^2n+mn^2 +m^2+2mn = 2018m + 2019n + 2019$$are as many as ...


p11. Given a triangle $ABC$ with $\angle ABC =135^o$ and $BC> AB$. Point $D$ lies on the side $BC$ so that $AB=CD$. Suppose $F$ is a point on the side extension $AB$ so that $DF$ is perpendicular to $AB$. The point $E$ lies on the ray $DF$ such that $DE> DF$ and $\angle ACE = 45^o$. The large angle $\angle AEC$ is ...


p12. The set of $S$ consists of $n$ integers with the following properties: For every three different members of $S$ there are two of them whose sum is a member of $S$. The largest value of $n$ is ....


p13. The minimum value of $\frac{a^2+2b^2+\sqrt2}{\sqrt{ab}}$ with $a, b$ positive reals is ....


p14. The polynomial P satisfies the equation $P (x^2) = x^{2019} (x+ 1) P (x)$ with $P (1/2)= -1$ is ....


p15. Look at a chessboard measuring $19 \times 19$ square units. Two plots are said to be neighbors if they both have one side in common. Initially, there are a total of $k$ coins on the chessboard where each coin is only loaded exactly on one square and each square can contain coins or blanks. At each turn. You must select exactly one plot that holds the minimum number of coins in the number of neighbors of the plot and then you must give exactly one coin to each neighbor of the selected plot. The game ends if you are no longer able to select squares with the intended conditions. The smallest number of $k$ so that the game never ends for any initial square selection is ....
13 replies
parmenides51
Nov 11, 2021
SomeonecoolLovesMaths
3 hours ago
Diophantine Equation in (x^2+4) set
Johann Peter Dirichlet   0
4 hours ago
Let $S=\{n^2+4 | n \in \mathbb{Z}\}$.

Find all $p,q,r \in S$ so that $pq-r=4$.
0 replies
Johann Peter Dirichlet
4 hours ago
0 replies
easy problem
lgx57   1
N 4 hours ago by rchokler
Let $x+y=3$ , $\frac{1}{x^2+y}+\frac{1}{x+y^2}=\frac{1}{2}$. Find the value of $x^5+y^5$.
1 reply
lgx57
5 hours ago
rchokler
4 hours ago
Ihave a minor issue.
CovertQED   0
5 hours ago
The area of triangle ABC is 18,sin2A +sin2B =4sinAsinB.Find the minimum perimeter of triangle ABC.
0 replies
CovertQED
5 hours ago
0 replies
2 points construction, incircle (In the World of Mathematics 478)
parmenides51   0
Apr 17, 2020
Point $A$ lies on the circle $\omega$ and point $X$ lies inside or outside this circle. Construct points $B$ and $C$ on $\omega$ such that point $X$ is the center of incircle or cirumcircle of triangle $ABC$.

(I. Kushnir, Kyiv)
0 replies
parmenides51
Apr 17, 2020
0 replies
2 points construction, incircle (In the World of Mathematics 478)
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parmenides51
30630 posts
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Point $A$ lies on the circle $\omega$ and point $X$ lies inside or outside this circle. Construct points $B$ and $C$ on $\omega$ such that point $X$ is the center of incircle or cirumcircle of triangle $ABC$.

(I. Kushnir, Kyiv)
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