Plan ahead for the next school year. Schedule your class today!

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k a July Highlights and 2025 AoPS Online Class Information
jwelsh   0
Jul 1, 2025
We are halfway through summer, so be sure to carve out some time to keep your skills sharp and explore challenging topics at AoPS Online and our AoPS Academies (including the Virtual Campus)!

[list][*]Over 60 summer classes are starting at the Virtual Campus on July 7th - check out the math and language arts options for middle through high school levels.
[*]At AoPS Online, we have accelerated sections where you can complete a course in half the time by meeting twice/week instead of once/week, starting on July 8th:
[list][*]MATHCOUNTS/AMC 8 Basics
[*]MATHCOUNTS/AMC 8 Advanced
[*]AMC Problem Series[/list]
[*]Plus, AoPS Online has a special seminar July 14 - 17 that is outside the standard fare: Paradoxes and Infinity
[*]We are expanding our in-person AoPS Academy locations - are you looking for a strong community of problem solvers, exemplary instruction, and math and language arts options? Look to see if we have a location near you and enroll in summer camps or academic year classes today! New locations include campuses in California, Georgia, New York, Illinois, and Oregon and more coming soon![/list]

MOP (Math Olympiad Summer Program) just ended and the IMO (International Mathematical Olympiad) is right around the corner! This year’s IMO will be held in Australia, July 10th - 20th. Congratulations to all the MOP students for reaching this incredible level and best of luck to all selected to represent their countries at this year’s IMO! Did you know that, in the last 10 years, 59 USA International Math Olympiad team members have medaled and have taken over 360 AoPS Online courses. Take advantage of our Worldwide Online Olympiad Training (WOOT) courses
and train with the best! Please note that early bird pricing ends August 19th!
Are you tired of the heat and thinking about Fall? You can plan your Fall schedule now with classes at either AoPS Online, AoPS Academy Virtual Campus, or one of our AoPS Academies around the US.

Our full course list for upcoming classes is below:
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0 replies
jwelsh
Jul 1, 2025
0 replies
Show that For any number to be a perfect square, it's coprime factors must be pe
Vulch   1
N 11 minutes ago by Mathzeus1024
Show that For any number to be a perfect square, it's coprime factors must be perfect square as well.
1 reply
Vulch
Sep 27, 2024
Mathzeus1024
11 minutes ago
Trigonometry equation practice
ehz2701   20
N an hour ago by vanstraelen
There is a lack of trigonometric bash practice, and I want to see techniques to do these problems. So here are 10 kinds of problems that are usually out in the wild. How do you tackle these problems? (I had ChatGPT write a code for this.). Please give me some general techniques to solve these kinds of problems, especially set 2b. I’ll add more later.

Leaderboard and Solved Problems

problem set 1a (1-10)

problem set 2a (1-20)

problem set 2b (1-20)
answers 2b

General techniques so far:

Trick 1: one thing to keep in mind is

[center] $\frac{1}{2} = \cos 36 - \sin 18$. [/center]

Many of these seem to be reducible to this. The half can be written as $\cos 60 = \sin 30$, and $\cos 36 = \sin 54$, $\sin 18 = \cos 72$. This is proven in solution 1a-1. We will refer to this as Trick 1.
20 replies
ehz2701
Jul 12, 2025
vanstraelen
an hour ago
Number Theory (Divisibility)
AbdulWaheed   4
N an hour ago by Mathzeus1024
Find all triples (a, b, c) of natural numbers such that the numbers $a^2$ + bc, $b^2$ + ac,
and $c^2$ + ab are powers of 2. (source, Sozopol 2023, Grades 8-9)
4 replies
AbdulWaheed
Jul 15, 2025
Mathzeus1024
an hour ago
[PMO27 Areas] I.15 why is this here
BinariouslyRandom   3
N 5 hours ago by tapilyoca
Find the sum of all prime numbers $p$ such that
\[ p \mid 2^{p^2+3p+2} + 3^{p^2+3p+2}. \]
3 replies
BinariouslyRandom
Jan 25, 2025
tapilyoca
5 hours ago
[PMO24 Qualifying II.9] Modulo 2477
kae_3   2
N 6 hours ago by tapilyoca
Find the sum of all positive integers $n$, $1\leq n\leq 5000$, for which $$n^2+2475n+2454+(-1)^n$$is divisible by $2477$. (Note that $2477$ is a prime number.)

Answer Confirmation
2 replies
kae_3
Feb 17, 2025
tapilyoca
6 hours ago
[PMO25 Areas I.18] P Divides Everything
kae_3   2
N Today at 4:40 AM by tapilyoca
Suppose that $p$ is a prime number which divides infinitely many numbers of the form $10^{n!}+2023$ where $n$ is a positive integer. What is the sum of all possible values of $p$?

Answer Confirmation
2 replies
kae_3
Feb 23, 2025
tapilyoca
Today at 4:40 AM
2015 mathtastic Mock AIME #3 min sum (1 - x)/(1 + x) for x+y+z=1
parmenides51   5
N Today at 3:12 AM by mathprodigy2011
The positive $x,y,z$ satisfy $x + y + z = 1$. If the minimum possible value of $\frac{1 - x}{1 + x}+ \frac{1-y}{1 + y}
+ \frac{1 - z}{1 + z}$ equals $\frac{m}{n}$, find $10m + n$.

Proposed by vincenthuang75025
5 replies
parmenides51
Dec 11, 2023
mathprodigy2011
Today at 3:12 AM
Inequalities
sqing   0
Today at 2:03 AM
Let $ a,b,c\geq 0  . $ Prove that
$$ \sqrt{ a^3+b^3+c^3+\frac{1}{4}} +  \frac{9}{5}abc+\frac{1}{2} \geq a+b+c$$O706
0 replies
sqing
Today at 2:03 AM
0 replies
Minimal of xy subjected to a constraint!
persamaankuadrat   9
N Today at 1:28 AM by ChickensEatGrass
Let $x,y$ be positive real numbers such that

$$x+y^{2}+x^{3} = 1481$$
Find the minimal value of $xy$
9 replies
persamaankuadrat
Thursday at 1:44 PM
ChickensEatGrass
Today at 1:28 AM
AoPS Intermediate Number Theory Course
Amazingatmath.com   3
N Today at 1:25 AM by Bummer12345
Hello,

I am thinking of taking the AoPS Intermediate Number Theory Course.

Does anyone have any feedback/advice on whether to take the course or not, related to the class or any other aspects?

For reference, I am going into 7th grade and got a 21 on 2025 AMC 8 and 79.5 on a mock 2024 AMC 10B. I am also doing AoPS vol 1, aops inter algebra, and aops intro to c&p.
3 replies
Amazingatmath.com
Yesterday at 4:59 PM
Bummer12345
Today at 1:25 AM
Inequalities
sqing   14
N Today at 1:14 AM by sqing
Let $ a,b,c\geq 0  $ and $ ab+bc+ca=2. $ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1} \geq 9-3\sqrt{6}$$Let $ a,b,c\geq 0  $ and $ ab+bc+ca=4. $ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1} \geq 6\sqrt{3}-9$$Let $ a,b,c\geq 0  $ and $ ab+bc+ca=6. $ Prove that
$$\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1} \geq 3(\sqrt{2}-1)$$Let $ a,b,c\geq 0  $ and $ ab+bc+ 3c^2=7. $ Prove that
$$ \frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}+\frac{1}{ 3c+1}\geq \frac{3}{ 2}$$
14 replies
sqing
Thursday at 1:49 PM
sqing
Today at 1:14 AM
The Circle of Incenters
justalonelyguy   3
N Today at 12:34 AM by mathprodigy2011
Let $ABC$ be a triangle such that $AB=AC$ let $D$ be a point in $BC$ and $M$ is the midpoint of $BC$ and let $I$ and $J$ the incenter of $\triangle ABD$ and $\triangle ACD$ Prove that $I,D,M,J$ are concyclic
3 replies
justalonelyguy
Yesterday at 3:06 AM
mathprodigy2011
Today at 12:34 AM
a + b + c + \fracs
SYBARUPEMULA   5
N Today at 12:30 AM by nudinhtien
Given $a, b, c > 0$ such that $9a + 5b + 9c = 218$,
find the smallest value of

$$a + b + c + \frac{40}{a + 6} + \frac{72}{b + 8} + \frac{10}{c + 2}$$
5 replies
SYBARUPEMULA
Jul 16, 2025
nudinhtien
Today at 12:30 AM
Power of point
mathisreal   1
N Today at 12:27 AM by mathprodigy2011
Let $ABCD$ be a paralellogram with $AB=8$ and $BC=4$. The circle $\Gamma$ passes by $A,C,M$ where $M$ is the midpoint of $BC$. The point $P\neq C$ is the intersection of $\Gamma$ and the line $CD$. The line $AD$ is tangent to $\Gamma$. Determine the length of the segment $PM$.
Brazil District MO 2015 #2
1 reply
mathisreal
Today at 12:15 AM
mathprodigy2011
Today at 12:27 AM
Advanced Floor Function in Number Theory
kisah_sangjuara   10
N Feb 26, 2025 by littleduckysteve
Problem. Prove or disprove that for any $n\in \mathbb{N}$, the value of $\left\lfloor\frac{2^n}{n}\right\rfloor$ is always even!
Notes. Here $\lfloor x \rfloor$ denotes the largest integer that is less than or equal to $x$
10 replies
kisah_sangjuara
Feb 1, 2025
littleduckysteve
Feb 26, 2025
Advanced Floor Function in Number Theory
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kisah_sangjuara
8 posts
#1 • 1 Y
Y by Lankou
Problem. Prove or disprove that for any $n\in \mathbb{N}$, the value of $\left\lfloor\frac{2^n}{n}\right\rfloor$ is always even!
Notes. Here $\lfloor x \rfloor$ denotes the largest integer that is less than or equal to $x$
This post has been edited 2 times. Last edited by kisah_sangjuara, Feb 2, 2025, 10:38 AM
Reason: Wrong assertion, you can find the counter example
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aidan0626
2069 posts
#2
Y by
n=12 $~~~~~~$
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martianrunner
226 posts
#3
Y by
thats crazy
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AbhayAttarde01
1583 posts
#4
Y by
i just saw this and did every number up to 20
then I hit 12
this equation, with n=12
will result in $341$, a contradiction
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littleduckysteve
468 posts
#5
Y by
Do you guys think that there might be more contridictions?
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hunterlyh
7 posts
#6
Y by
n=25,it will result in1342177
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martianrunner
226 posts
#8
Y by
guys, I made a code that finds contradictions, and I tried it up to $1,000$ (after that it gives an error, because $2^n$, where $n$ is greater than $1,000$ is quite large and apparently is too large for integer division), and the only contradictions it found were $12, 25, 45,$ and $48$. I'm wondering if there are any other contradictions other than these four...

This is my code by the way, if it can be optimized I would appreciate suggestions (it is written in python)

n = int(input())
counter = 0
for i in range(1, n+1):
    if (((2**i)/i) - int((2**i)/i)) < 0.5 and int((2**i)/i) % 2 == 1:
        counter += 1
        print(i)
print(counter)
This post has been edited 1 time. Last edited by martianrunner, Feb 2, 2025, 3:41 AM
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aidan0626
2069 posts
#9
Y by
erm
my code testing the first 50 got 12, 18, 25, 36, 42, 45, 48
i just did ((2**n)//n)%2
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anduran
486 posts
#10 • 2 Y
Y by aidan0626, Sedro
Funny how a problem you were meant to prove turned into who can disprove it the hardest
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martianrunner
226 posts
#11
Y by
oh wait lol why did I think that the problem was asking the nearest integer instead of the floor function
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littleduckysteve
468 posts
#12
Y by
Well if n is a integer power of two it has to be even.
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