2024 Chile National Olympiad.

1

Let \( f(x) = \frac{100^x}{100^x + 10} \). Determine the value of: \[ f\left( \frac{1}{2024} \right) - f\left( \frac{2}{2024} \right) + f\left( \frac{3}{2024} \right) - f\left( \frac{4}{2024} \right) + \ldots - f\left( \frac{2022}{2024} \right) + f\left( \frac{2023}{2024} \right) \]

2

On a table, there are many coins and a container with two coins. Vale and Diego play the following game, where Vale starts and then Diego plays, alternating turns. If at the beginning of a turn the container contains \( n \) coins, the player can add a number \( d \) of coins, where \( d \) divides exactly into \( n \) and \( d < n \). The first player to complete at least 2024 coins in the container wins. Prove that there exists a strategy for Vale to win, no matter the decisions made by Diego.

3

Let \( AD \) and \( BE \) be altitudes of triangle \( \triangle ABC \) that meet at the orthocenter \( H \). The midpoints of segments \( AB \) and \( CH \) are \( X \) and \( Y \), respectively. Prove that the line \( XY \) is perpendicular to line \( DE \).

4

Find all pairs \((x, y)\) of real numbers that satisfy the system \[ (x + 1)(x^2 + 1) = y^3 + 1 \]\[ (y + 1)(y^2 + 1) = x^3 + 1 \]

5

You have a collection of at least two tokens where each one has a number less than or equal to 10 written on it. The sum of the numbers on the tokens is \( S \). Find all possible values of \( S \) that guarantee that the tokens can be separated into two groups such that the sum of each group does not exceed 80.

6

Let \( 133\ldots 33 \) be a number with \( k \geq 2 \) digits, which we assume is prime. Prove that \( k(k + 2) \) is a multiple of 24. (For example, 133...33 is a prime number when \( k = 16\)