Difference between revisions of "2023 RMO"

(Problem 2)
(Problem 4)
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==Problem 4==
 
==Problem 4==
 
For any natural number <math>n</math>, expressed in base <math>10</math>, let <math>s(n)</math> denote the sum of all its digits. Find all natural numbers <math>m</math> and <math>n</math> such that <math>m < n</math> and
 
For any natural number <math>n</math>, expressed in base <math>10</math>, let <math>s(n)</math> denote the sum of all its digits. Find all natural numbers <math>m</math> and <math>n</math> such that <math>m < n</math> and
<cmath>(s(n))^{2} = m</cmath> and <cmath>(s(m))^{2} = n</cmath>.
+
 
 +
<math>(s(n))^{2} = m</math> and <math>(s(m))^{2} = n</math>.
  
 
==Problem 5==
 
==Problem 5==

Revision as of 09:01, 2 November 2024

Problem 1

Let $\mathbb{N}$ be the set of all positive integers and $S = {(a,b,c,d)  \in  \mathbb{N}^{4} : a^{2} + b^{2} + c^{2} = d^{2}}$. Find the largest positive integer $m$ such that $m$ divides $abcd$ for all $(a,b,c,d)  \in S$.

Problem 2

Let $\omega$ be a semicircle with $AB$ as the bounding diameter and let $CD$ be a variable chord of the semicircle of constant length such that $C,D$ lie in the interior of the arc $AB$. Let $E$ be a point on the diameter $AB$ such that $CE$ and $DE$ are equally inclined to the line $AB$. Prove that

(a) the measure of $\angle CED$ is a constant;

(b) the circumcircle of triangle $CED$ passes through a fixed point.

Problem 3

Problem 4

For any natural number $n$, expressed in base $10$, let $s(n)$ denote the sum of all its digits. Find all natural numbers $m$ and $n$ such that $m < n$ and

$(s(n))^{2} = m$ and $(s(m))^{2} = n$.

Problem 5

Problem 6

Consider a set of $16$ points arranged in a $4\times4$ square grid formation. Prove that if any $7$ of these points are coloured blue, then there exists an isosceles right-angled triangle whose vertices are all blue.