Inspired by Omerking

by sqing, Apr 16, 2025, 5:11 AM

Let $ a,b,c>0 $ and $  ab+bc+ca\geq \dfrac{1}{3}. $ Prove that
$$  ka+ b+kc\geq \sqrt{\frac{4k-1}{3}}$$Where $ k\geq 1.$$$  4a+ b+4c\geq \sqrt{5}$$
This post has been edited 1 time. Last edited by sqing, 3 hours ago

Interesting inequalities

by sqing, Apr 16, 2025, 3:36 AM

Let $ a,b,c\geq  0 $ and $  ab+bc+ca+abc=4$ . Prove that
$$k(a+b+c) -ab-bc\geq 4\sqrt{k(k+1)}-(k+4)$$Where $ k\geq \frac{16}{9}. $
$$ \frac{16}{9}(a+b+c) -ab-bc\geq  \frac{28}{9}$$
This post has been edited 1 time. Last edited by sqing, 2 hours ago

A Segment Bisection Problem

by buratinogigle, Apr 16, 2025, 1:36 AM

In triangle $ABC$, let the incircle $\omega$ touch sides $BC, CA, AB$ at $D, E, F$, respectively. Let $P$ lie on the line through $D$ perpendicular to $BC$. Let $Q, R$ be the intersections of $PC, PB$ with $EF$, respectively. Let $K, L$ be the projections of $R, Q$ onto line $BC$. Let $M, N$ be the second intersections of $DQ, DR$ with the incircle $\omega$. Let $S$ be the intersection of $KM$ and $LN$. Prove that the line $DS$ bisects segment $QR$.
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Weird Inequality Problem

by Omerking, Apr 15, 2025, 8:56 AM

Following inequality is given:
$$3\geq ab+bc+ca\geq \dfrac{1}{3}$$Find the range of values that can be taken by :
$1)a+b+c$
$2)abc$

Where $a,b,c$ are positive reals.
This post has been edited 1 time. Last edited by Omerking, Yesterday at 9:18 AM

NEPAL TST 2025 DAY 2

by Tony_stark0094, Apr 12, 2025, 8:40 AM

Consider an acute triangle $\Delta ABC$. Let $D$ and $E$ be the feet of the altitudes from $A$ to $BC$ and from $B$ to $AC$ respectively.

Define $D_1$ and $D_2$ as the reflections of $D$ across lines $AB$ and $AC$, respectively. Let $\Gamma$ be the circumcircle of $\Delta AD_1D_2$. Denote by $P$ the second intersection of line $D_1B$ with $\Gamma$, and by $Q$ the intersection of ray $EB$ with $\Gamma$.

If $O$ is the circumcenter of $\Delta ABC$, prove that $O$, $D$, and $Q$ are collinear if and only if quadrilateral $BCQP$ can be inscribed within a circle.

$\textbf{Proposed by Kritesh Dhakal, Nepal.}$
This post has been edited 1 time. Last edited by Tony_stark0094, Apr 13, 2025, 12:37 AM
Reason: typo

NEPAL TST DAY 2 PROBLEM 2

by Tony_stark0094, Apr 12, 2025, 8:37 AM

Kritesh manages traffic on a $45 \times 45$ grid consisting of 2025 unit squares. Within each unit square is a car, facing either up, down, left, or right. If the square in front of a car in the direction it is facing is empty, it can choose to move forward. Each car wishes to exit the $45 \times 45$ grid.

Kritesh realizes that it may not always be possible for all the cars to leave the grid. Therefore, before the process begins, he will remove $k$ cars from the $45 \times 45$ grid in such a way that it becomes possible for all the remaining cars to eventually exit the grid.

What is the minimum value of $k$ that guarantees that Kritesh's job is possible?

$\textbf{Proposed by Shining Sun. USA}$
This post has been edited 2 times. Last edited by Tony_stark0094, Apr 13, 2025, 3:12 AM
Reason: typo

NEPAL TST DAY-2 PROBLEM 1

by Tony_stark0094, Apr 12, 2025, 8:34 AM

Let the sequence $\{a_n\}_{n \geq 1}$ be defined by
\[
a_1 = 1, \quad a_{n+1} = a_n + \frac{1}{\sqrt[2024]{a_n}} \quad \text{for } n \geq 1, \, n \in \mathbb{N}
\]Prove that
\[
a_n^{2025} >n^{2024}
\]for all positive integers $n \geq 2$.

$\textbf{Proposed by Prajit Adhikari, Nepal.}$
This post has been edited 1 time. Last edited by Tony_stark0094, Apr 13, 2025, 12:36 AM
Reason: typo

Hard number theory

by Hip1zzzil, Mar 30, 2025, 5:08 AM

Positive integers $a, b$ satisfy both of the following conditions.
For a positive integer $m$, if $m^2 \mid ab$, then $m = 1$.
There exist integers $x, y, z, w$ that satisfies the equation $ax^2 + by^2 = z^2 + w^2$ and $z^2 + w^2 > 0$.
Prove that there exist integers $x, y, z, w$ that satisfies the equation $ax^2 + by^2 + n = z^2 + w^2$, for each integer $n$.
This post has been edited 4 times. Last edited by Hip1zzzil, Mar 30, 2025, 1:07 PM
Reason: Better

Constant Angle Sum

by i3435, May 11, 2021, 1:06 PM

Let $ABC$ be a triangle with circumcircle $\Omega$, $A$-angle bisector $l_A$, and $A$-median $m_A$. Suppose that $l_A$ meets $\overline{BC}$ at $D$ and meets $\Omega$ again at $M$. A line $l$ parallel to $\overline{BC}$ meets $l_A$, $m_A$ at $G$, $N$ respectively, so that $G$ is between $A$ and $D$. The circle with diameter $\overline{AG}$ meets $\Omega$ again at $J$.

As $l$ varies, show that $\angle AMN + \angle DJG$ is constant.

MP8148

2017 PAMO Shortlsit: Power of a prime is a sum of cubes

by DylanN, May 5, 2019, 8:46 PM

For which prime numbers $p$ can we find three positive integers $n$, $x$ and $y$ such that $p^n = x^3 + y^3$?

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  • dj so orz :omighty:

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  • legendary problem writer

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  • orz $$\,$$

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  • waiting for a recap of your amc proposals for this year :D

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  • also happy late bday man! i missed it by 2 days but hope you are enjoyed it

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  • :love: tfw kakuro appears on amc :love:

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  • Hi dj :)

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  • Roses are red,
    Wolfram is banned,
    The best problem writer is
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  • hello :)

    by aidan0626, Jul 26, 2022, 5:49 PM

  • Do you have a link to your main blog that you started after graduating from high school, I couldn't find it. @dj I met you IRL at Awesome Math summer Program several years ago.

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