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k a March Highlights and 2025 AoPS Online Class Information
jlacosta   0
Mar 2, 2025
March is the month for State MATHCOUNTS competitions! Kudos to everyone who participated in their local chapter competitions and best of luck to all going to State! Join us on March 11th for a Math Jam devoted to our favorite Chapter competition problems! Are you interested in training for MATHCOUNTS? Be sure to check out our AMC 8/MATHCOUNTS Basics and Advanced courses.

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Do you have plans this summer? There are so many options to fit your schedule and goals whether attending a summer camp or taking online classes, it can be a great break from the routine of the school year. Check out our summer courses at AoPS Online, or if you want a math or language arts class that doesn’t have homework, but is an enriching summer experience, our AoPS Virtual Campus summer camps may be just the ticket! We are expanding our locations for our AoPS Academies across the country with 15 locations so far and new campuses opening in Saratoga CA, Johns Creek GA, and the Upper West Side NY. Check out this page for summer camp information.

Be sure to mark your calendars for the following events:
[list][*]March 5th (Wednesday), 4:30pm PT/7:30pm ET, HCSSiM Math Jam 2025. Amber Verser, Assistant Director of the Hampshire College Summer Studies in Mathematics, will host an information session about HCSSiM, a summer program for high school students.
[*]March 6th (Thursday), 4:00pm PT/7:00pm ET, Free Webinar on Math Competitions from elementary through high school. Join us for an enlightening session that demystifies the world of math competitions and helps you make informed decisions about your contest journey.
[*]March 11th (Tuesday), 4:30pm PT/7:30pm ET, 2025 MATHCOUNTS Chapter Discussion MATH JAM. AoPS instructors will discuss some of their favorite problems from the MATHCOUNTS Chapter Competition. All are welcome!
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0 replies
jlacosta
Mar 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
deduction from function
MetaphysicalWukong   2
N 4 minutes ago by MetaphysicalWukong
can we then deduce that h has exactly 1 zero?
2 replies
MetaphysicalWukong
39 minutes ago
MetaphysicalWukong
4 minutes ago
A lot of tangent circle
ItzsleepyXD   0
5 minutes ago
Source: Own
Let \( \triangle ABC \) be a triangle with circumcircle \( \omega \) and circumcenter \( O \). Let \( \omega_A \) and \( I_A \) represent the \( A \)-excircle and \( A \)-excenter, respectively. Denote by \( \omega_B \) the circle tangent to \( AB \), \( BC \), and \( \omega \) on the arc \( BC \) not containing \( A \), and similarly for \( \omega_C \). Let the tangency points of \( \omega_A, \omega_B, \omega_C \) with line \( BC \) be \( X, Y, Z \), respectively. Let \( P \neq A \) be the intersection point of \( (AYZ) \) and \( \omega \). Define \( Q \) as the point on segment \( OI_A \) such that \( 2 \cdot OQ = QI_A \). Suppose that \( XP \) intersects \( \omega \) again at \( R \). Let \( T \) be the touch point of the \( A \)-mixtilinear incircle and \( \omega \), and let \( A' \) be the antipode of \( A \) with respect to \( \omega \). Let \( S \) be the intersection of \( A'Q \) and \( I_AT \).

Show that the line \( RS \) is the radical axis of \( \omega_B \) and \( \omega_C \).
0 replies
ItzsleepyXD
5 minutes ago
0 replies
weird FE on R
frac   4
N 10 minutes ago by NicoN9
Source: probably own
Find all functions $f:\mathbb{R} \rightarrow \mathbb{R}$ such that
$$f(x+y)^2=xf(x+f(y))+yf(f(y))+f(xy)$$for all $x,y\in \mathbb{R}$.
4 replies
+1 w
frac
Jan 4, 2025
NicoN9
10 minutes ago
number theory question?
jag11   3
N 15 minutes ago by Anabcde
Find the smallest positive integer n such that n is a multiple of 11, n +1 is a multiple of 10, n + 2 is a
multiple of 9, n + 3 is a multiple of 8, n +4 is a multiple of 7, n +5 is a multiple of 6, n +6 is a multiple of
5, n + 7 is a multiple of 4, n + 8 is a multiple of 3, and n + 9 is a multiple of 2.

I tried doing the mods and simplifying it but I'm kinda confused.
3 replies
jag11
Yesterday at 10:41 PM
Anabcde
15 minutes ago
Circles and Chords
steven_zhang123   0
29 minutes ago
(1) Let \( A \) , \( B \) and \( C \) be points on circle \( O \) divided into three equal parts. Construct three equal circles \( O_1 \), \( O_2 \), and \( O_3 \) tangent to \( O \) internally at points \( A \), \( B \), and \( C \) respectively. Let \( P \) be any point on arc \( AC \), and draw tangents \( PD \), \( PE \), and \( PF \) to circles \( O_1 \), \( O_2 \), and \( O_3 \) respectively. Prove that \( PE = PD + PF \).

(2) Let \( A_1 \), \( A_2 \), \( \cdots \), \( A_n \) be points on circle \( O \) divided into \( n \) equal parts. Construct \( n \) equal circles \( O_1 \), \( O_2 \), \( \cdots \), \( O_n \) tangent to \( O \) internally at \( A_1 \), \( A_2 \), \( \cdots \), \( A_n \). Let \( P \) be any point on circle \( O \), and draw tangents \( PB_1 \), \( PB_2 \), \( \cdots \), \( PB_n \) to circles \( O_1 \), \( O_2 \), \( \cdots \), \( O_n \). If the sum of \( k \) of \( PB_1 \), \( PB_2 \), \( \cdots \), \( PB_n \) equals the sum of the remaining \( n-k \) (where \( n \geq k \geq 1 \)), find all such \( n \).
0 replies
steven_zhang123
29 minutes ago
0 replies
Integer FE
GreekIdiot   1
N 43 minutes ago by pco
Let $\mathbb{N}$ denote the set of positive integers
Find all $f: \mathbb{N} \rightarrow \mathbb{N}$ such that for all $a,b \in \mathbb{N}$ it holds that $f(ab+f(b-1))|bf(a+b)f(3b-2+a)$
1 reply
GreekIdiot
Yesterday at 8:53 PM
pco
43 minutes ago
Double factorial inequality
Snoop76   2
N an hour ago by Snoop76
Source: own
Show that: $$2n \cdot \sum_{k=0}^n (2k-1)!!{n\choose k}>\sum_{k=0}^n (2k+1)!!{n\choose k}$$Note: consider $(-1)!!=1$ and $n>1$
2 replies
Snoop76
Feb 7, 2025
Snoop76
an hour ago
Algebra Problem
JetFire008   1
N an hour ago by aidan0626
Find the sum of the series
$$1^2-2^2+3^2-4^2+...+(-1)^n+1n^2$$
1 reply
JetFire008
2 hours ago
aidan0626
an hour ago
Hyperbolic tangent
MetaphysicalWukong   6
N 2 hours ago by MetaphysicalWukong
Source: Kunwei Ding
Consider the function below. Can someone explain to me why that is the correct answer and find the value of a?
6 replies
MetaphysicalWukong
2 hours ago
MetaphysicalWukong
2 hours ago
Inequality with real numbers
JK1603JK   4
N 2 hours ago by SunnyEvan
Source: unknown
Let a,b,c are real numbers. Prove that (a^3+b^3+c^3+3abc)^4+(a+b+c)^3(a+b-c)^3(-a+b+c)^3(a-b+c)^3>=0
4 replies
JK1603JK
Yesterday at 6:48 AM
SunnyEvan
2 hours ago
Interesting inequality
sqing   1
N 2 hours ago by SunnyEvan
Source: Own
Let $ a,b,c\geq 0,(ab+c)(ac+b)\neq 0 $ and $ a+b+c=3 . $ Prove that
$$ \frac{1}{ab+c+k}+\frac{1}{ac+b+k} \geq\frac{2}{k+2} $$Where $ k\geq 0. $
1 reply
sqing
5 hours ago
SunnyEvan
2 hours ago
Interesting inequality
sqing   2
N 2 hours ago by SunnyEvan
Source: Own
Let $ a,b,c\geq 0,(ab+c)(ac+b)\neq 0 $ and $ a+b+c=3 . $ Prove that
$$ \frac{1}{ab+kc}+\frac{1}{ac+kb} \geq\frac{4}{3k} $$Where $ k\geq 3. $
$$ \frac{1}{ab+2c}+\frac{1}{ac+2b} \geq\frac{16}{25} $$$$ \frac{1}{ab+3c}+\frac{1}{ac+3b} \geq\frac{4}{9} $$$$ \frac{1}{ab+4c}+\frac{1}{ac+4b} \geq\frac{1}{3} $$

2 replies
sqing
4 hours ago
SunnyEvan
2 hours ago
Prove that P1(x), P2(x) ,... Pn(x) = k has no root
truongphatt2668   1
N 3 hours ago by removablesingularity
Let $n \in \mathbb{N}^*$ and $P_1(x),P_2(x), \ldots P_n(x) \in \mathbb{Z}[x]$ such that $\mathrm{deg} P_i = 2, \forall i = \overline{1,n}$. Prove that exists many $k \in \mathbb{N}$ such that every equation: $P_i(x) = k, \forall i = \overline{1,n}$ has no real roots
1 reply
truongphatt2668
6 hours ago
removablesingularity
3 hours ago
Transitive relation
MetaphysicalWukong   1
N 3 hours ago by removablesingularity
Source: Huabing Dai
Let ? be the relation on the set of integers, where (?, ?) ∈ ? if ? + ? is even.
Is ? transitive?

I know ? is reflexive and symmetric but not sure about transitivity.
1 reply
MetaphysicalWukong
4 hours ago
removablesingularity
3 hours ago
Geometry Problem #42
vankhea   2
N Friday at 7:05 PM by kaede_Arcadia
Source: Van Khea
Let $P$ be any point. Let $D, E, F$ be projection point from $P$ to $BC, CA, AB$. Circumcircle $(ABC)$ cuts circumcircle $(AEF), (BFD), (CDE)$ at $A_1, B_1, C_1$. Let $A_2, B_2, C_2$ be antipode of $A_1, B_1, C_1$ wrt $(AEF), (BFD), (CDE)$. Prove that $A_2, B_2, C_2, P$ are cyclic.
2 replies
vankhea
Sep 6, 2023
kaede_Arcadia
Friday at 7:05 PM
Geometry Problem #42
G H J
G H BBookmark kLocked kLocked NReply
Source: Van Khea
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vankhea
894 posts
#1
Y by
Let $P$ be any point. Let $D, E, F$ be projection point from $P$ to $BC, CA, AB$. Circumcircle $(ABC)$ cuts circumcircle $(AEF), (BFD), (CDE)$ at $A_1, B_1, C_1$. Let $A_2, B_2, C_2$ be antipode of $A_1, B_1, C_1$ wrt $(AEF), (BFD), (CDE)$. Prove that $A_2, B_2, C_2, P$ are cyclic.
Z K Y
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Paramizo_Dicrominique
275 posts
#2 • 1 Y
Y by vankhea
Let $AA_1,BB_1,CC_1$ intersecting forming $\triangle{XYZ}$. By isogonal conjugate and pedal circle we get that $AA_2,BB_2,CC_2$ are concurrent at $W$ isogonal conjugate to $P$ wrt. $\triangle{XYZ}$. Following the Miquel structure for $\triangle{WAB}$ so $W,A_2,P,B_2$ lie on a circle. Similarly so $P,C_2,A_2,W$ lie on a circle. By simple angle chasing so $A_2,B_2,C_2,P,W$ lie on a circle.
$Q.E.D.$
Z K Y
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kaede_Arcadia
17 posts
#3
Y by
Obviously, $A_2,B_2,C_2,P$ are equidistant from the circumcenter of $ \triangle ABC$.
Z K Y
N Quick Reply
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