Complicated FE

by XAN4, Apr 23, 2025, 11:53 AM

Find all solutions for the functional equation $f(xyz)+\sum_{cyc}f(\frac{yz}x)=f(x)\cdot f(y)\cdot f(z)$, in which $f$: $\mathbb R^+\rightarrow\mathbb R^+$
Note: the solution is actually quite obvious - $f(x)=x^n+\frac1{x^n}$, but the proof is important.
Note 2: it is likely that the result can be generalized into a more advanced questions, potentially involving more bash.

Feet of perpendiculars to diagonal in cyclic quadrilateral

by jl_, Apr 23, 2025, 10:42 AM

Suppose $ABCD$ is a cyclic quadrilateral with $\angle ABC = \angle ADC = 90^{\circ}$. Let $E$ and $F$ be the feet of perpendiculars from $A$ and $C$ to $BD$ respectively. Prove that $BE = DF$.

Erasing a and b and replacing them with a - b + 1

by jl_, Apr 23, 2025, 10:38 AM

Ruby writes the numbers $1, 2, 3, . . . , 10$ on the whiteboard. In each move, she selects two distinct numbers, $a$ and $b$, erases them, and replaces them with $a+b-1$. She repeats this process until only one number, $x$, remains. What are all the possible values of $x$?

Find maximum area of right triangle

by jl_, Apr 23, 2025, 10:33 AM

Given a right-angled triangle with hypothenuse $2024$, find the maximal area of the triangle.

x^3+y^3 is prime

by jl_, Apr 23, 2025, 10:28 AM

Find all pairs of positive integers $(x,y)$, so that the number $x^3+y^3$ is a prime.

Prove that sum of 1^3+...+n^3 is a square

by jl_, Apr 23, 2025, 10:12 AM

Prove that for all positive integers $n$, $1^3 + 2^3 + 3^3 +\dots+n^3$ is a perfect square.
This post has been edited 3 times. Last edited by jl_, 3 hours ago
Reason: Change subject and source
L

interesting function equation (fe) in IR

by skellyrah, Apr 23, 2025, 9:51 AM

2021 EGMO P1: {m, 2m+1, 3m} is fantabulous

by anser, Apr 13, 2021, 12:00 PM

The number 2021 is fantabulous. For any positive integer $m$, if any element of the set $\{m, 2m+1, 3m\}$ is fantabulous, then all the elements are fantabulous. Does it follow that the number $2021^{2021}$ is fantabulous?

#14) IMO 2014 P4

by sa2001, Feb 19, 2018, 3:10 PM

Problem statement

A proof using phantom point N' and Pascal's Theorem -
This post has been edited 2 times. Last edited by pro_4_ever, Feb 19, 2018, 4:42 PM

IMO Shortlist 2014 N5

by hajimbrak, Jul 11, 2015, 9:09 AM

Find all triples $(p, x, y)$ consisting of a prime number $p$ and two positive integers $x$ and $y$ such that $x^{p -1} + y$ and $x + y^ {p -1}$ are both powers of $p$.

Proposed by Belgium
This post has been edited 3 times. Last edited by hajimbrak, Jul 23, 2015, 10:51 AM
Reason: Added proposer

Integer a_k such that b - a^n_k is divisible by k

by orl, Jul 13, 2008, 1:41 PM

Let $b,n > 1$ be integers. Suppose that for each $k > 1$ there exists an integer $a_k$ such that $b - a^n_k$ is divisible by $k$. Prove that $b = A^n$ for some integer $A$.

Author: Dan Brown, Canada
This post has been edited 3 times. Last edited by v_Enhance, Jan 18, 2016, 2:13 AM
Reason: Fix obsolete TeX

You can either Bash or Think..... Choose Wisely

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  • Hey, what a nice blog!!!!! :D

    by Power_Set, Jun 24, 2018, 9:53 PM

  • Is your blog dead ? No new post in almost 2 months.

    My blog has died due to malnutrition of problems. :P

    by integrated_JRC, May 2, 2018, 5:52 AM

  • @ below, I will do it soon

    by pro_4_ever, Mar 1, 2018, 10:37 AM

  • Hi, I think we should 'hide' our solutions, as it is difficult to go up and down the blog :D

    by Drunken_Master, Mar 1, 2018, 10:36 AM

  • Yeah, I created a test blog, it seems to be an AoPS problem not CSS, can't do anything about it. I'll post it in site support forum later.

    by Vrangr, Feb 20, 2018, 5:48 AM

  • The problem is not in the CSS, I believe, as the CSS only looks after the appearance of the blog, and not the $\text{\LaTeX}$ rendering.

    by WizardMath, Feb 19, 2018, 11:34 PM

  • I'll fix the CSS after boards of need be (I'll probably be starting my own blog too then)

    by Vrangr, Feb 19, 2018, 4:41 PM

  • @ below,
    Pls ask WizardMath...
    The CSS is taken from his amazing Blog, "An Olympiad Journey"...
    I know nothing abt programming.
    (BTW I got permission for taking the CSS. No Copyright Issues!)

    by pro_4_ever, Feb 19, 2018, 4:16 PM

  • Huge flaw in website design: comment gets erased if while typing $\LaTeX$ has an error and needs to be fixed.

    by Vrangr, Feb 19, 2018, 12:26 PM

  • Upon WizardMath's Request, let us all post synthetic solutions. Well, let's declare that this blog is intended to give the reader some good problems with simple synthetic solutions. All the best. Not trying to be rude,but I might delete upcoming Bashes :)

    by pro_4_ever, Feb 13, 2018, 4:50 PM

  • Here's an idea. Ban all bashes on this blog from now on. Also try posting your own previous geo solutions as storage (I hope this is allowed). This would make the quality of the blog better. Bashes are basically write-once, read-never things. Why bother?

    by WizardMath, Feb 13, 2018, 4:33 PM

  • Somebody type Egmo 2013 Problem 1.
    No bash,purely troll problem.:)

    by QWERTYphysics, Feb 13, 2018, 4:11 PM

  • I hate having to see a pure geometry blog being swamped to death with bashes.

    Obviously a bash is a super terrible idea. Don't do one.
    Unless you are bad at synthetic.

    by WizardMath, Feb 13, 2018, 2:58 PM

  • @ayan Done:)

    by pro_4_ever, Feb 13, 2018, 1:38 PM

  • 9th shout :P

    by MEGAKNIGHT, Feb 13, 2018, 11:23 AM

  • @below Pls don't post a bash if you are thinking about posting a new entry!

    by pro_4_ever, Feb 13, 2018, 11:11 AM

  • Wait, I thought bash is frowned upon in this blog.

    by WizardMath, Feb 12, 2018, 6:57 PM

  • Hmmm...
    Combi Geometry is accepted...

    by pro_4_ever, Feb 10, 2018, 7:32 AM

  • Can we post Combi here?

    by ayan.nmath, Feb 10, 2018, 7:31 AM

  • Parag dey

    by Paragdey12, Feb 6, 2018, 1:17 PM

  • More posts please :icecream:

    by AnArtist, Feb 6, 2018, 2:38 AM

  • Second Shout!

    by ccx09, Feb 3, 2018, 9:20 PM

  • 1st shout! :D

    by AnArtist, Jan 31, 2018, 9:20 AM

23 shouts
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