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Contests & Programs AMC and other contests, summer programs, etc.
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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.

Are you ready to level up with Olympiad training? Registration is open with early bird pricing available for our WOOT programs: MathWOOT (Levels 1 and 2), CodeWOOT, PhysicsWOOT, and ChemWOOT. What is WOOT? WOOT stands for Worldwide Online Olympiad Training and is a 7-month high school math Olympiad preparation and testing program that brings together many of the best students from around the world to learn Olympiad problem solving skills. Classes begin in September!

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!
[*]March 13th (Thursday), 4:00pm PT/7:00pm ET, Free Webinar about Summer Camps at the Virtual Campus. Transform your summer into an unforgettable learning adventure! From elementary through high school, we offer dynamic summer camps featuring topics in mathematics, language arts, and competition preparation - all designed to fit your schedule and ignite your passion for learning.[/list]
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0 replies
jlacosta
Mar 2, 2025
0 replies
combo j3 :blobheart:
rhydon516   21
N 12 minutes ago by CatinoBarbaraCombinatoric
Source: USAJMO 2025/3
Let $m$ and $n$ be positive integers, and let $\mathcal R$ be a $2m\times 2n$ grid of unit squares.

A domino is a $1\times2$ or $2\times1$ rectangle. A subset $S$ of grid squares in $\mathcal R$ is domino-tileable if dominoes can be placed to cover every square of $S$ exactly once with no domino extending outside of $S$. Note: The empty set is domino tileable.

An up-right path is a path from the lower-left corner of $\mathcal R$ to the upper-right corner of $\mathcal R$ formed by exactly $2m+2n$ edges of the grid squares.

Determine, with proof, in terms of $m$ and $n$, the number of up-right paths that divide $\mathcal R$ into two domino-tileable subsets.
21 replies
rhydon516
Mar 20, 2025
CatinoBarbaraCombinatoric
12 minutes ago
Tennessee Math Tournament (TMT) Online 2025
TennesseeMathTournament   35
N 41 minutes ago by athreyay
Hello everyone! We are excited to announce a new competition, the Tennessee Math Tournament, created by the Tennessee Math Coalition! Anyone can participate in the virtual competition for free.

The testing window is from March 22nd to April 5th, 2025. Virtual competitors may participate in the competition at any time during that window.

The virtual competition consists of three rounds: Individual, Bullet, and Team. The Individual Round is 60 minutes long and consists of 30 questions (AMC 10 level). The Bullet Round is 20 minutes long and consists of 80 questions (Mathcounts Chapter level). The Team Round is 30 minutes long and consists of 16 questions (AMC 12 level). Virtual competitors may compete in teams of four, or choose to not participate in the team round.

To register and see more information, click here!

If you have any questions, please email connect@tnmathcoalition.org or reply to this thread!

Thank you to our lead sponsor, Jane Street!

IMAGE
35 replies
TennesseeMathTournament
Mar 9, 2025
athreyay
41 minutes ago
USA Canada math camp
Bread10   25
N an hour ago by akliu
How difficult is it to get into USA Canada math camp? What should be expected from an accepted applicant in terms of the qualifying quiz, essays and other awards or math context?
25 replies
Bread10
Mar 2, 2025
akliu
an hour ago
funny title placeholder
pikapika007   47
N 2 hours ago by llddmmtt1
Source: USAJMO 2025/6
Let $S$ be a set of integers with the following properties:
[list]
[*] $\{ 1, 2, \dots, 2025 \} \subseteq S$.
[*] If $a, b \in S$ and $\gcd(a, b) = 1$, then $ab \in S$.
[*] If for some $s \in S$, $s + 1$ is composite, then all positive divisors of $s + 1$ are in $S$.
[/list]
Prove that $S$ contains all positive integers.
47 replies
pikapika007
Yesterday at 12:10 PM
llddmmtt1
2 hours ago
Derivative of function R^2 to R^2
Sifan.C.Maths   0
Today at 7:09 AM
Source: Internet
Give a function $f:\mathbb{R}^2 \to \mathbb{R}^2: f(x,y)=(x^2+xy,y^2+x)$. Calculate the first and second derivative of the function at the point $(1,-1)$.
0 replies
Sifan.C.Maths
Today at 7:09 AM
0 replies
some distribution
We2592   2
N Today at 6:46 AM by Tricky123
Let \( F(x) \) be a distribution function. Prove that for any \( h \neq 0 \), the function

\[
G(x) = \frac{1}{2h} \int_{x-h}^{x+h} F(t) \, dt
\]
is also a distribution function.



how to approach?
2 replies
We2592
Yesterday at 1:07 PM
Tricky123
Today at 6:46 AM
Equation with complex numbers on the unit circle
Tintarn   9
N Today at 4:30 AM by Fibonacci_math
Source: IMC 2024, Problem 1
Determine all pairs $(a,b) \in \mathbb{C} \times \mathbb{C}$ of complex numbers satisfying $|a|=|b|=1$ and $a+b+a\overline{b} \in \mathbb{R}$.
9 replies
Tintarn
Aug 7, 2024
Fibonacci_math
Today at 4:30 AM
numerical analysis
ay19bme   1
N Today at 3:05 AM by YuLuo
...............
1 reply
ay19bme
Yesterday at 4:48 PM
YuLuo
Today at 3:05 AM
distribution function
We2592   1
N Yesterday at 9:55 PM by alexheinis
Q)The distribution function $F(x)$ of a variate $X$ is defined as follows:
\[
F(x) =
\begin{cases} 
A, & -\infty < x < -1, \\
B, & -1 \leq x < 0, \\
C, & 0 \leq x < 2, \\
D, & 2 \leq x < \infty.
\end{cases}
\]
where $A,B,C,D$ are constants. Determine the values of $A,B,C,D$ it being given that $P(X=0)=\frac{1}{6}$ and $P(X>1)=\frac{2}{3}$

how to solve
1 reply
We2592
Yesterday at 1:23 PM
alexheinis
Yesterday at 9:55 PM
Complex roots
Sarbajit10598   7
N Yesterday at 5:57 PM by quasar_lord
Source: C.M.I entrance exam 2019
2.(a)Count the number of all the complex roots $\omega$ of the equation $z^{2019}-1=0$ which follows $$|\omega+1|\geq \sqrt{2+\sqrt{2}}$$(b) Solve for real $x$
$$\frac{8^x+27^x}{12^x+18^x}=\frac{7}{6}$$
7 replies
Sarbajit10598
May 15, 2019
quasar_lord
Yesterday at 5:57 PM
CMI Entrance 19#3
bubu_2001   12
N Yesterday at 5:17 PM by quasar_lord
Evaluate $\int_{ 0 }^{ \infty } ( 1 + x^2 )^{-( m + 1 )} \mathrm{d}x$ where $m \in \mathbb{N} $
12 replies
bubu_2001
Oct 31, 2019
quasar_lord
Yesterday at 5:17 PM
analysis
ay19bme   2
N Yesterday at 3:27 PM by ay19bme
..........
2 replies
ay19bme
Thursday at 8:06 PM
ay19bme
Yesterday at 3:27 PM
Do these have a closed form?
Entrepreneur   0
Yesterday at 2:17 PM
Source: Own
$$\int_0^\infty\frac{t^{n-1}}{(t+\alpha)^2+m^2}dt.$$$$\int_0^\infty\frac{e^{nt}}{(t+\alpha)^2+m^2}dt.$$$$\int_0^\infty\frac{dx}{(1+x^a)^m(1+x^b)^n}.$$
0 replies
Entrepreneur
Yesterday at 2:17 PM
0 replies
more rafinament limits integrals
teomihai   6
N Yesterday at 2:11 PM by teomihai
Let$ f:[0,1]->R$ continously function with $f'$ bounded
Find $$\lim_{n \rightarrow \infty}n(n\int_{0}^{1}x^{n}f(x)dx-f(1))$$
6 replies
teomihai
Yesterday at 4:55 AM
teomihai
Yesterday at 2:11 PM
high tech FE as J1?!
imagien_bad   56
N Yesterday at 10:45 PM by eg4334
Source: USAJMO 2025/1
Let $\mathbb Z$ be the set of integers, and let $f\colon \mathbb Z \to \mathbb Z$ be a function. Prove that there are infinitely many integers $c$ such that the function $g\colon \mathbb Z \to \mathbb Z$ defined by $g(x) = f(x) + cx$ is not bijective.
Note: A function $g\colon \mathbb Z \to \mathbb Z$ is bijective if for every integer $b$, there exists exactly one integer $a$ such that $g(a) = b$.
56 replies
imagien_bad
Mar 20, 2025
eg4334
Yesterday at 10:45 PM
high tech FE as J1?!
G H J
G H BBookmark kLocked kLocked NReply
Source: USAJMO 2025/1
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Sedro
5812 posts
#43
Y by
Assume for the sake of contradiction that there exists a function $f:\mathbb{Z}\to \mathbb{Z}$ such that $g(x) = f(x)+cx$ is not bijective for only finitely many integers $c$. We prove a key fact about $f$.

Claim: The value of $f(x+1)-f(x)$ can only take on a finite number of integer values.

Proof: Suppose otherwise; we show that $g(x)$ fails to be injective, and hence bijective, for infinitely many integer values of $c$, which is the desired contradiction. Suppose that $f(a+1)-f(a) = d$ for integers $a$ and $d$. Let $c = -d$; this implies that $g(a+1)=f(a+1)+c(a+1) = f(a)+ca = g(a)$. Hence $g(x)=f(x)+cx$ fails to be injective for this particular value of $c$. Since $d$ can take on infinitely many integer values, there are infinitely many integers $c$ such that $g(x) = f(x)+cx$ is not injective. $\blacksquare$

Thus, let $S$ be the set of all possible values of $f(x+1)-f(x)$, and let $k$ denote the largest absolute value of an element of $S$. To finish. we now claim that for all integers $c \ge k+2$, $g(x)=f(x)+cx$ fails to be surjective, and hence bijective. Recall that we have $|f(x+1)-f(x)| \le k$ for all integers $x$. When $c \ge k+2$, we have $g(x+1)-g(x) = f(x+1)-f(x) + c\ge 2$. This clearly implies that $g(x)=f(x)+cx$ fails to be surjective for all $c\ge k+2$, which finishes the problem. $\blacksquare$
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djmathman
7935 posts
#44
Y by
Sketch: Consider the set
\[
\mathcal D := \{f(n+1) - f(n): n\in\mathbb Z\}.
\]If $\mathcal D$ is infinite, then $x\mapsto f(x) + cx$ isn't injective for any $c\in\mathcal D$. If $\mathcal D$ is finite, then $x\mapsto f(x) + cx$ isn't surjective for any $c\gg  \max\mathcal D$.
This post has been edited 2 times. Last edited by djmathman, Thursday at 8:35 PM
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Pitchu-25
53 posts
#45
Y by
Suppose for the sake of contradiction that there exists an integer constant $M$ with the property that $\vert c\vert \ge M$ implies $f(x)+cx$ is bijective.

Claim : For any integer $x$, we have $\vert f(x+1)-f(x)\vert<M$.
Proof : Otherwise, $c=f(x)-f(x+1)$ gives $g(x+1)=g(x)$ which contradicts injectivity. $\square$

Now, translate $f$ so that $f(0)=0$ ; this clearly doesn't change the problem. By triangle inequality, the claim yields $\vert f(k)\vert=\vert f(k)-f(0)\vert<k\times M$ for every $k$. Therefore, the function $f(x)+Mx$ does not attain $0$, contradicting surjectivity.
$\blacksquare$
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gladIasked
620 posts
#46
Y by
solved j2 and proceeded to get stuck on this for 3.5 hours :coolspeak:
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blueprimes
306 posts
#47
Y by
"little bit of this, little bit of that" ahh problem
I think this solution is the most natural to think of, I find that this problem would be hard for newer oly contestants, but quite standard for anyone that does a decent amount of oly prep

$\textbf{Claim 1:}$ If $f$ is a bijection, there exists a $c > 0$ where $g(x) \equiv f(x) + cx$ is not bijective.
Proof. If $f$ is increasing, then clearly it must be of the form $f(x) \equiv x + k$ for some constant $k$, so $g(x) \equiv (c + 1)x + k$. Then set $c = 1434!$ and choose a $y$-value that is not $k \pmod{1434! + 1}$, this is obviously unattainable so $g$ is not bijective.

On the other hand, if $f$ is not increasing, there exists an integer $m$ where $f(m) > f(m + 1)$ so setting $c = f(m) - f(m + 1)$ yields $g(m) = g(m + 1)$ so $g$ is obviously not bijective.

Now we're home, for the sake of contradiction assume there are a finite number of $c$ where $g$ is not bijective. Then there exists a sufficiently large $\ell$ where for all $c \ge \ell$ then $g$ is bijective. But setting $f(x) + \ell x \mapsto f(x)$ in $\textbf{Claim 1}$ violates this, contradiction. BOOM.
This post has been edited 5 times. Last edited by blueprimes, Yesterday at 10:57 AM
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MathLuis
1459 posts
#48 • 1 Y
Y by Pengu14
This being JMO is kinda crazy, still it died quickly so cool ig.
Suppose FTSOC that for all $|c| \ge N$ it happens that $g$ was bijective, then $g(a+1)=g(a)$ if and only if $-c=f(a+1)-f(a)$ and thus from here we know that $|f(x+1)-f(x)|<N$, so now let $c=N+1$ then $g(x+1)-g(x)=f(x+1)-f(x)+N+1 \ge 2$ for all integers $x$, and thus $g(1) \ge g(0)+2$ and so on we get $g(n) \ge g(0)+2n$ for all positive integers $n$ therefore $g(0)+1$ is not achieved on the positive side but also notice that $g(x+1) \ge g(x)$ and therefore $g(x) \le g(0)$ for all negative $x$ and $g(0) \ne g(0)+1$, therefore $g(0)+1$ is never attained contradicting bijectivity of $g$ for this case which is claimed to work, contradiction!, therefore such infinite $c$ exist and we are done :cool:.
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Super_AA
173 posts
#49
Y by
Here's my solution. Can you tell me if it is rigorous
Click to reveal hidden text
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Maximilian113
504 posts
#50
Y by
FAKESOLVE:

Suppose that $f(x)$ is linear. Then we can write $f(x)=ax+b,$ so every integer attained by $g(x)$ is congruent to $b \pmod {a+b},$ so the problem is clear.

Now assume that $f(x)$ is not linear. We show that there exist infinitely many $c$ such that $g(x)$ is not injective. Observe that for $a \neq b,$ $$f(a)+ca = f(b)+cb \iff c=-\frac{f(a)-f(b)}{a-b}.$$It suffices to show that the RHS can attain infinitely many values. For the sake of a contradiction assume otherwise.

Consider some point $(x, f(x)).$ Then connecting this point to all other points $(y, f(y)),$ and taking the union yields a finite set of lines (at least 2). But by the Pigeonhole principle, some line $\ell$ has infinitely many points on it, so considering a point $P$ on another line distinct from $\ell$ we see that connecting $P$ to each point $K$ on $\ell$ we are able to attain infinitely many slopes. This is a contradiction. QED
This post has been edited 2 times. Last edited by Maximilian113, Yesterday at 4:00 AM
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eg4334
614 posts
#51 • 1 Y
Y by Maximilian113
Maximilian113 wrote:
This is less of an algebraic proof.

Suppose that $f(x)$ is linear. Then we can write $f(x)=ax+b,$ so every integer attained by $g(x)$ is congruent to $b \pmod {a+b},$ so the problem is clear.

Now assume that $f(x)$ is not linear. We show that there exist infinitely many $c$ such that $g(x)$ is not injective. Observe that for $a \neq b,$ $$f(a)+ca = f(b)+cb \iff c=-\frac{f(a)-f(b)}{a-b}.$$It suffices to show that the RHS can attain infinitely many values. For the sake of a contradiction assume otherwise.

Consider some point $(x, f(x)).$ Then connecting this point to all other points $(y, f(y)),$ and taking the union yields a finite set of lines (at least 2). But by the Pigeonhole principle, some line $\ell$ has infinitely many points on it, so considering a point $P$ on another line distinct from $\ell$ we see that connecting $P$ to each point $K$ on $\ell$ we are able to attain infinitely many slopes. This is a contradiction. QED

Unless I am understanding this proof wrong, further elaboration would need to show why this infinite number of slopes would all be integers because $c$ must be an integer. I went down a similar path in test but could not finish.
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Maximilian113
504 posts
#52 • 1 Y
Y by eg4334
oops :blush: mb ur right.. @above
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Maximilian113
504 posts
#53
Y by
Ok, maybe this works instead?

Consider the set of values $f(x+1)-f(x)$ can attain as $x$ varies. If this is an infinite set, by my above logic we are done.

Instead, assume that there are only a finite amount of values, $r_1, r_2, \cdots, r_k.$ Then $$g(x+1)-g(x)=f(x+1)-f(x)+c=r_i+c,$$so each increment is of the form $r_i+c$ and making $c$ arbitrarily large $g(x)$ cannot attain $g(0)+1,$ so $g(x)$ is not surjective.
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sepehr2010
102 posts
#54
Y by
Claim: Let $A$ be the set of all non-zero $a_k$ where $a_k = f(k+1) - f(k)$ as $k$ varies. This must be an infinite set.

Proof: Assume the contrary. Then, $g(k+1) - g(k) = f(k+1) - f(k) + c = a_k + c$ for some $k$. For this to be surjective, $g(0)+1 = $ sum of elements of B $- c|B|$, where $B$ is some subset of $A$. Notice that as we send $c$ to be greater than or equal to the largest element of $B$ + 1434, this will not be surjective. Thus, there are infinitely many values of $c$ such that this is not bijective.

Claim: If $c = -a_k$ (or is any element of $A$), $g(x)$ will not be bijective.
Proof: Take $g(k+1) = f(k+1) - c(k+1)$ and $g(k) = f(k) - c(k)$. Notice that $g(k+1) - g(k) = f(k+1) - f(k) + c = 0$. Thus, this is not injective. As a result, since $A$ has infinitely many elements, we are done.
,
This post has been edited 2 times. Last edited by sepehr2010, Yesterday at 10:18 PM
Reason: funny number
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LearnMath_105
134 posts
#55
Y by
Maximilian113 wrote:
FAKESOLVE:

Suppose that $f(x)$ is linear. Then we can write $f(x)=ax+b,$ so every integer attained by $g(x)$ is congruent to $b \pmod {a+b},$ so the problem is clear.

Now assume that $f(x)$ is not linear. We show that there exist infinitely many $c$ such that $g(x)$ is not injective. Observe that for $a \neq b,$ $$f(a)+ca = f(b)+cb \iff c=-\frac{f(a)-f(b)}{a-b}.$$It suffices to show that the RHS can attain infinitely many values. For the sake of a contradiction assume otherwise.


Consider some point $(x, f(x)).$ Then connecting this point to all other points $(y, f(y)),$ and taking the union yields a finite set of lines (at least 2). But by the Pigeonhole principle, some line $\ell$ has infinitely many points on it, so considering a point $P$ on another line distinct from $\ell$ we see that connecting $P$ to each point $K$ on $\ell$ we are able to attain infinitely many slopes. This is a contradiction. QED


expected points for this?
This post has been edited 1 time. Last edited by LearnMath_105, Yesterday at 6:17 PM
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cosinesine
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Consider the set $S$ given by all numbers of the form $f(x) - f(x + 1)$. If we set $c = f(x) - f(x + 1)$, then $g(x) = g(x + 1)$, so $g$ is not a bijection. Therefore $S$ is a finite set. Let $s$ be the maximal element of $S$.

We show that taking $c > |s| + 1$ produces $g$ not a bijection, from which the result follows. Note that $g(x + 1) - g(x) = f(x + 1) - f(x) + c = -r + c$ for some $r \in S$. However by our construction $-r + c > 1$, so $g$ is strictly increasing and moreover the differences between terms are all $> 1$. However, this implies that $g(x) + 1 \neq g(y)$ for all y, and so $g$ is not a surjection, as desired.
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eg4334
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LearnMath_105 wrote:
Maximilian113 wrote:
FAKESOLVE:

Suppose that $f(x)$ is linear. Then we can write $f(x)=ax+b,$ so every integer attained by $g(x)$ is congruent to $b \pmod {a+b},$ so the problem is clear.

Now assume that $f(x)$ is not linear. We show that there exist infinitely many $c$ such that $g(x)$ is not injective. Observe that for $a \neq b,$ $$f(a)+ca = f(b)+cb \iff c=-\frac{f(a)-f(b)}{a-b}.$$It suffices to show that the RHS can attain infinitely many values. For the sake of a contradiction assume otherwise.


Consider some point $(x, f(x)).$ Then connecting this point to all other points $(y, f(y)),$ and taking the union yields a finite set of lines (at least 2). But by the Pigeonhole principle, some line $\ell$ has infinitely many points on it, so considering a point $P$ on another line distinct from $\ell$ we see that connecting $P$ to each point $K$ on $\ell$ we are able to attain infinitely many slopes. This is a contradiction. QED


expected points for this?

should be 0 because it completely ignores that c is an integer, and the intended solution is completely different and does not use graph analysis
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