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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
Binomial Sum
P162008   0
2 hours ago
Compute $\sum_{r=0}^{n} \sum_{k=0}^{r} (-1)^k (k + 1)(k + 2) \binom {n + 5}{r - k}$
0 replies
P162008
2 hours ago
0 replies
Triple Sum
P162008   0
3 hours ago
Find the value of

$\sum_{k=1}^{\infty} \frac{(-1)^{k+1}}{k} \sum_{n=0}^{\infty} \sum_{m=0}^{\infty} \frac{(-1)^m}{k.2^n + 2m + 1}$
0 replies
P162008
3 hours ago
0 replies
Binomial Sum
P162008   0
3 hours ago
The numbers $p$ and $q$ are defined in the following manner:

$p = 99^{98} - \frac{99}{1} 98^{98} + \frac{99.98}{1.2} 97^{98} - \frac{99.98.97}{1.2.3} 96^{98} + .... + 99$

$q = 99^{100} - \frac{99}{1} 98^{100} + \frac{99.98}{1.2} 97^{100} - \frac{99.98.97}{1.2.3} 96^{100} + .... + 99$

If $p + q = k(99!)$ then find the value of $\frac{k}{10}.$
0 replies
P162008
3 hours ago
0 replies
Polynomial Limit
P162008   0
3 hours ago
If $P_{n}(x) = \prod_{k=0}^{n} \left(x + \frac{1}{2^k}\right) = \sum_{k=0}^{n} a_{k} x^k$ then find the value of $\lim_{n \to \infty} \frac{a_{n - 2}}{a_{n - 4}}.$
0 replies
P162008
3 hours ago
0 replies
Telescopic Sum
P162008   0
3 hours ago
Compute the value of $\Omega = \sum_{r=1}^{\infty} \frac{14 - 9r - 90r^2 - 36r^3}{7^r  r(r + 1)(r + 2)(4r^2 - 1)}$
0 replies
P162008
3 hours ago
0 replies
Theory of Equations
P162008   0
4 hours ago
Let $a,b,c,d$ and $e\in [-2,2]$ such that $\sum_{cyc} a = 0, \sum_{cyc} a^3 = 0, \sum_{cyc} a^5 = 10.$ Find the value of $\sum_{cyc} a^2.$
0 replies
P162008
4 hours ago
0 replies
Can a 0-1 matrix square to the matrix with all ones?
Tintarn   3
N 6 hours ago by Kugelmonster
Source: IMC 2024, Problem 3
For which positive integers $n$ does there exist an $n \times n$ matrix $A$ whose entries are all in $\{0,1\}$, such that $A^2$ is the matrix of all ones?
3 replies
Tintarn
Aug 7, 2024
Kugelmonster
6 hours ago
CHINA TST 2017 P6 DAY1
lingaguliguli   0
6 hours ago
When i search the china TST 2017 problem 6 day I i crossed out this lemme, but don't know to prove it, anyone have suggestion? tks
Given a fixed number n, and a prime p. Let f(x)=(x+a_1)(x+a_2)...(x+a_n) in which a_1,a_2,...a_n are positive intergers. Show that there exist an interger M so that 0<v_p((f(M))< n + v_p(n!)
0 replies
lingaguliguli
6 hours ago
0 replies
Math and physics camp
Snezana242   0
Today at 8:53 AM
Discover IMPSC 2025: International Math & Physics Summer Camp!

Are you a high school student (grades 9–12) with a passion for Physics and Math?
Join the IMPSC 2025, an online summer camp led by top IIT professors, offering a college-level education in Physics and Math.

What Can You Expect?

Learn advanced topics from renowned IIT professors

Connect with students worldwide

Strengthen your college applications

Get a recommendation letter for top universities!

How to Apply & More Info
For all the details you need about the camp, dates, application process, and more, visit our official website:
https://www.imc-impea.org/IMC/index.php

Don't miss out on this opportunity to elevate your academic journey!
Apply now and take your education to the next level.
0 replies
Snezana242
Today at 8:53 AM
0 replies
Two times derivable real function
Valentin Vornicu   11
N Today at 7:26 AM by solyaris
Source: RMO 2008, 11th Grade, Problem 3
Let $ f: \mathbb R \to \mathbb R$ be a function, two times derivable on $ \mathbb R$ for which there exist $ c\in\mathbb R$ such that
\[ \frac { f(b)-f(a) }{b-a} \neq f'(c) ,\] for all $ a\neq b \in \mathbb R$.

Prove that $ f''(c)=0$.
11 replies
Valentin Vornicu
Apr 30, 2008
solyaris
Today at 7:26 AM
Limit with sin^2x
Quantum_fluctuations   7
N Today at 7:25 AM by P162008

Evaluate:

$\lim_{x \to 0} \left( 1^{1/\sin^2 x} + 2^{1/\sin^2 x} + 3^{1/\sin^2 x} + .  .  . + n^{1/\sin^2 x} \right)^{\sin^2 x}$
7 replies
Quantum_fluctuations
Apr 26, 2020
P162008
Today at 7:25 AM
Decimal number defined recursively by digit sums modulo 10
fermion13pi   2
N Today at 7:20 AM by solyaris
Source: Competição Elon Lages Lima
Consider the real number written in decimal notation:
r = 0.235831...
where, starting from the third digit after the decimal point, each digit is equal to the remainder when the sum of the previous two digits is divided by 10.

Which of the following statements is true?

(a) (10⁶⁰ - 1).r is an integer
(b) (10²⁵ - 1).r is an integer
(c) (10¹⁷ - 1).r is an integer
(d) r is an irrational algebraic number
(e) r is an irrational transcendental number

(Recall that a complex number is called algebraic if it is a root of a non-zero polynomial with integer coefficients.)
2 replies
fermion13pi
Yesterday at 11:14 PM
solyaris
Today at 7:20 AM
Combinatoric
spiderman0   1
N Today at 6:44 AM by MathBot101101
Let $ S = \{1, 2, 3, \ldots, 2024\}.$ Find the maximum positive integer $n \geq 2$ such that for every subset $T \subset S$ with n elements, there always exist two elements a, b in T such that:

$|\sqrt{a} - \sqrt{b}| < \frac{1}{2} \sqrt{a - b}$
1 reply
spiderman0
Yesterday at 7:46 AM
MathBot101101
Today at 6:44 AM
Combinatorial proof
MathBot101101   10
N Today at 6:20 AM by MathBot101101
Is there a way to prove
\frac{1}{(1+1)!}+\frac{2}{(2+1)!}+...+\frac{n}{(n+1)!}=1-\frac{1}{{n+1)!}
without induction and using only combinatorial arguments?

Induction proof wasn't quite as pleasing for me.
10 replies
MathBot101101
Apr 20, 2025
MathBot101101
Today at 6:20 AM
Easy matrix equation involving invertibility
Ciobi_   2
N Apr 3, 2025 by Moubinool
Source: Romania NMO 2025 11.2
Let $n$ be a positive integer, and $a,b$ be two complex numbers such that $a \neq 1$ and $b^k \neq 1$, for any $k \in \{1,2,\dots ,n\}$. The matrices $A,B \in \mathcal{M}_n(\mathbb{C})$ satisfy the relation $BA=a I_n + bAB$. Prove that $A$ and $B$ are invertible.
2 replies
Ciobi_
Apr 2, 2025
Moubinool
Apr 3, 2025
Easy matrix equation involving invertibility
G H J
Source: Romania NMO 2025 11.2
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Ciobi_
25 posts
#1
Y by
Let $n$ be a positive integer, and $a,b$ be two complex numbers such that $a \neq 1$ and $b^k \neq 1$, for any $k \in \{1,2,\dots ,n\}$. The matrices $A,B \in \mathcal{M}_n(\mathbb{C})$ satisfy the relation $BA=a I_n + bAB$. Prove that $A$ and $B$ are invertible.
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loup blanc
3583 posts
#2 • 1 Y
Y by MS_asdfgzxcvb
Read my post #2 in
https://artofproblemsolving.com/community/q1h2490224p20956569
Z K Y
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Moubinool
5567 posts
#3
Y by
loup blanc wrote:
Read my post #2 in
see
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