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k a August Highlights and 2025 AoPS Online Class Information
jwelsh   0
Aug 1, 2025
CONGRATULATIONS to all the competitors at this year’s International Mathematical Olympiad (IMO)! The US Team took second place with 5 gold medals and 1 silver - we are proud to say that each member of the 2025 IMO team has participated in an AoPS WOOT (Worldwide Online Olympiad Training) class!

"As a parent, I'm deeply grateful to AoPS. Tiger has taken very few math courses outside of AoPS, except for a local Math Circle that doesn't focus on Olympiad math. AoPS has been one of the most important resources in his journey. Without AoPS, Tiger wouldn't be where he is today — especially considering he's grown up in a family with no STEM background at all."
— Doreen Dai, parent of IMO US Team Member Tiger Zhang

Interested to learn more about our WOOT programs? Check out the course page here or join a Free Scheduled Info Session. Early bird pricing ends August 19th!:
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0 replies
jwelsh
Aug 1, 2025
0 replies
2^x+32^x=8^x+16^x (OTIS MOCK AIME 2025 II #3)
megahertz13   4
N 9 minutes ago by fruitmonster97
Let $x$ be the unique positive real number satisfying \[ 2^x+32^x=8^x+16^x. \]Compute $8^{x+2}-2^{x+6}$.

James Stewart
4 replies
megahertz13
Jan 22, 2025
fruitmonster97
9 minutes ago
A writing game
Ecrin_eren   3
N 11 minutes ago by Ecrin_eren


There is an integer greater than 1 written on the board in A’s house. Every morning when A wakes up, he erases the number n on the board and does the following:

If there is a positive integer m such that m^3= n, then he writes m on the board.

Otherwise, he writes 2n+1 on the board.


Since A repeats this process infinitely many times, prove that among all the numbers A has written and will write on the board, there are infinitely many greater than 10^100.





3 replies
Ecrin_eren
Jul 28, 2025
Ecrin_eren
11 minutes ago
Sequence
Ecrin_eren   3
N 12 minutes ago by Ecrin_eren


The sequence {an} for n from 1 to infinity is defined as follows:
a1 = 1,
a2 = 2^2
a3 = 3^(3^3)
a4 = 4^(4^(4^4))
and so on,

Accordingly, for which positive integers m does the sequence {an} take all possible values modulo m?




3 replies
Ecrin_eren
Jul 28, 2025
Ecrin_eren
12 minutes ago
Polynomial
Ecrin_eren   2
N 27 minutes ago by Ecrin_eren
P is a polynomial with real coefficients is called good if for any positive integers a,b [P(a)-P(b)]/a-b is an integer.P(0)=0 prove that there exists infinitely many good polynomials with non integer coefficients
2 replies
Ecrin_eren
Jul 28, 2025
Ecrin_eren
27 minutes ago
D1056 : This series converge ?
Dattier   3
N Today at 2:55 AM by Alphaamss
Source: les dattes à Dattier
Let $f$ increasing with the limit to $+\infty$ is $+\infty$.

The serie $\sum \limits_{n\geq 1} \dfrac{\cos(n)}{f(n+2025\times \cos(n))}$ converge ?
3 replies
Dattier
Aug 3, 2025
Alphaamss
Today at 2:55 AM
Matrix equation
Natrium   7
N Yesterday at 9:46 PM by Natrium
If $A$ is a complex matrix with $AA^*A=A^3,$ prove that $A$ is self-adjoint, i.e., that $A^*=A.$
7 replies
Natrium
Jul 12, 2025
Natrium
Yesterday at 9:46 PM
continuously differentiable function
enter16180   5
N Yesterday at 6:45 PM by Ilovesumona
Source: IMC 2025, Problem 6
Let $f:(0, \infty) \rightarrow \mathbb{R}$ be a continuously differentiable function, and let $b>a>0$ be real numbers such that $f(a)=f(b)=k$. Prove that there exists a point $\xi \in(a, b)$ such that
$$
f(\xi)-\xi f^{\prime}(\xi)=k
$$
5 replies
enter16180
Jul 31, 2025
Ilovesumona
Yesterday at 6:45 PM
Putnam 2008 A1
Kent Merryfield   45
N Yesterday at 5:45 PM by lpieleanu
Let $ f: \mathbb{R}^2\to\mathbb{R}$ be a function such that $ f(x,y)+f(y,z)+f(z,x)=0$ for real numbers $ x,y,$ and $ z.$ Prove that there exists a function $ g: \mathbb{R}\to\mathbb{R}$ such that $ f(x,y)=g(x)-g(y)$ for all real numbers $ x$ and $ y.$
45 replies
Kent Merryfield
Dec 8, 2008
lpieleanu
Yesterday at 5:45 PM
analysis
Hello_Kitty   0
Yesterday at 4:52 PM
What about of the uniform convergence of $ (f_n) $
(on a largest possible subset of $\mathbb{R}$) defined by :

$ \forall x,n, \; \int_0^{1/n}\frac {e^t dt}{t+f_n(x)}=x $ or

$ \forall x,n, \; \int_0^x\frac {e^t dt}{t+f_n(x)}=n $

- you may chose the formula you prefer, or study both ? -
0 replies
Hello_Kitty
Yesterday at 4:52 PM
0 replies
analysis
Hello_Kitty   4
N Yesterday at 2:37 PM by Hello_Kitty
Prove the density of the irrationals in the reals,
write it in one line.
4 replies
Hello_Kitty
Yesterday at 2:50 AM
Hello_Kitty
Yesterday at 2:37 PM
Prove direct sum in another way
SillinessSquared   2
N Yesterday at 12:26 PM by loup blanc
Source: Essential Linear Algebra, Titu Andresscu
(All equations written in Typst in a custom format then retyped in Latex; please excuse the odd syntax)

Let $V$ be a vector space over $F$ and $T: V --> V$ be a linear transformation such that $ \text{ker} T = \text{ker} T^2 $ and $Im T = Im T^2.$
Prove that $ V = \text{ker} T \oplus \text{Im} T. $

My friend solved this but he used the rank nullity theorem and didn't use the fact that Im T = Im T^2. I haven't learned that theorem, but I did learn about projections and their properties. Could someone help using the following definitions?

#example(number: [5.3])[#set enum(numbering : "a.")
7. We introduce a fundamental class of linear transformations: *projections onto subspaces.* Suppose $V$ is a vector space over a field $F$ and that $W_1,W_2$ are subspaces of $V$ such that $V = W_1 \oplus W_2$. The *projection onto $W_1$ along $W_2$* is the map $p: V -> W_1$ defined as follows: for each $v \in V, p(v) \in W_1: v - p(v) \in W_2$.

]

#theorem(number: [5.15])[#set enum(numbering : "a)")
Let $V$ be a vector space over a field $F$ and let $T: V --> V$ be a linear map on $V$. The following statements are equivalent:
+ $T$ is a projection
+ We have $T \circ T = T$. Moreover, if this is the case, then $\text{ker} T \oplus \text{Im} (T) = V$.
]
2 replies
SillinessSquared
Monday at 5:30 PM
loup blanc
Yesterday at 12:26 PM
min and max
aktyw19   3
N Yesterday at 10:36 AM by Mathzeus1024
find min and max f
a)
$x \ge 0, y \ge 0,3x+y \le 6,x+y \le 4$

$f=2x-3y$

b)
$x,y,z>0,x+y+z=1,x \le y,y \le z$

$f=2x+y-z$
3 replies
aktyw19
Dec 2, 2012
Mathzeus1024
Yesterday at 10:36 AM
The constant of $Si(\pi)$!
Alphaamss   0
Yesterday at 9:48 AM
Source: Own
I want to know that is the constant $$Si(\pi)=\int_0^\pi\frac{\sin x}{x}{\rm{d}}x$$irrational number or rational number? Any comments or hints will welcome!
0 replies
Alphaamss
Yesterday at 9:48 AM
0 replies
real numbers
Hello_Kitty   7
N Yesterday at 7:56 AM by P0tat0b0y
Are there some irrational $ a,b $ such that $ a^b $ is rational ?
7 replies
Hello_Kitty
Monday at 10:16 PM
P0tat0b0y
Yesterday at 7:56 AM
Function and Quadratic equations help help help
Ocean_MathGod   1
N May 20, 2025 by Mathzeus1024
Consider this parabola: y = x^2 + (2m + 1)x + m(m - 3) where m is constant and -1 ≤ m ≤ 4. A(-m-1, y1), B(m/2, y2), C(-m, y3) are three different points on the parabola. Now rotate the axis of symmetry of the parabola 90 degrees counterclockwise around the origin O to obtain line a. Draw a line from the vertex P of the parabola perpendicular to line a, meeting at point H.

1) express the vertex of the quadratic equation using an expression with m.
2) If, regardless of the value of m, the parabola and the line y=x−km (where k is a constant) have exactly one point of intersection, find the value of k.

3) (where I'm struggling the most) When 1 < PH ≤ 6, compare the values of y1, y2, and y3.
1 reply
Ocean_MathGod
Aug 26, 2024
Mathzeus1024
May 20, 2025
Function and Quadratic equations help help help
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Ocean_MathGod
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Consider this parabola: y = x^2 + (2m + 1)x + m(m - 3) where m is constant and -1 ≤ m ≤ 4. A(-m-1, y1), B(m/2, y2), C(-m, y3) are three different points on the parabola. Now rotate the axis of symmetry of the parabola 90 degrees counterclockwise around the origin O to obtain line a. Draw a line from the vertex P of the parabola perpendicular to line a, meeting at point H.

1) express the vertex of the quadratic equation using an expression with m.
2) If, regardless of the value of m, the parabola and the line y=x−km (where k is a constant) have exactly one point of intersection, find the value of k.

3) (where I'm struggling the most) When 1 < PH ≤ 6, compare the values of y1, y2, and y3.
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Mathzeus1024
1098 posts
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Part (I):

Completing the square on this parabola yields:

$y = \left(x+\frac{2m+1}{2}\right)^2 + m(m-3) - \frac{(2m+1)^2}{4} \Rightarrow y = \left(x+\frac{2m+1}{2}\right)^2 -\frac{16m+1}{4}$;

with vertex $\textcolor{red}{P\left(-\frac{2m+1}{2}, -\frac{16m+1}{4}\right)}$.

Part (II):

If the parabola intersects the line $y=x-km$ in exactly one point, then:

$x^2 + (2m+1)x + m(m-3) = x-km \Rightarrow x^2 +2mx + (m^2-3m+km) = 0 \Rightarrow x = \frac{-2m \pm \sqrt{4m^2-4(1)[m^2+(k-3)m]}}{2}$ (i);

of which we require the discriminant in (i) to equal zero. This occurs $\Leftrightarrow \textcolor{red}{k=3}$.

Part (III):

For $m \in [-1,4]$ we have the points $A(-m-1, -4m); B\left(\frac{m}{2}, \frac{9m^2-10m}{4}\right); C(-m,-4m)$ on the parabola. Checking $-4m=\frac{9m^2-10m}{4} \Rightarrow 9m^2-6m=m(9m+6)=0 \Rightarrow m = -\frac{2}{3}, 0$ gives us the orderings:

$y_{2}>y_{1}=y_{3}$ for $m \in \left[-1,-\frac{2}{3}\right) \cup (0,4]$;

$y_{2}=y_{1}=y_{3}$ for $m = -\frac{2}{3}, 0$;

$y_{2} < y_{1} = y_{3}$ for $m \in \left(-\frac{2}{3}, 0\right)$.

Rotating the parabola's axis of symmetry (i.e. $x= -\frac{2m+1}{2}$) $90^{\circ}$ counterclockwise about the origin gives us the horizontal line $y = -\frac{2m+1}{2}$ from which $|PH| = \left|-\frac{16m+1}{4} - \left(-\frac{2m+1}{2}\right)\right| = \frac{|1-12m|}{4}$.

If $1 < |PH| \le 6$, then $1 < \frac{|1-12m|}{4}\le 6 \Rightarrow m \in \left[-\frac{23}{12},-\frac{1}{4}\right) \cup \left(\frac{5}{12},\frac{25}{12}\right]$. This results in the following orderings:

$\textcolor{red}{y_{2}>y_{1}=y_{2}}$ for $\textcolor{red}{m \in \left[-1, -\frac{2}{3}\right) \cup \left(\frac{5}{12},\frac{25}{12}\right]}$;

$\textcolor{red}{y_{2}=y_{1}=y_{3}}$ for $\textcolor{red}{m = -\frac{2}{3}}$;

$\textcolor{red}{y_{2}<y_{1}=y_{3}}$ for $\textcolor{red}{m \in \left(-\frac{2}{3}, -\frac{1}{4}\right)}$.
This post has been edited 6 times. Last edited by Mathzeus1024, May 31, 2025, 1:03 PM
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