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Thinking Out Loud – EGMO 2014 Problem 3

EGMO 2014, Problem 3. We denote the number of positive divisors of a positive integer \(m\) by \(d(m)\) and the number of distinct prime divisors of \(m\) by \(\omega(m)\). Let \(k\) be a positive integer. Prove that there exist infinitely many positive integers \(n\) such that \(\omega(n) = k\) and \(d(n)\) does not divide \(d(a^2+b^2)\) for any positive integers \(a, b\) satisfying \(a + b = n\).

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Thinking Out Loud – EGMO 2014 Problem 2

EGMO 2014, problem 2. Let \(D\) and \(E\) be points in the interiors of sides \(AB\) and \(AC\), respectively, of a triangle \(ABC\), such that \(DB=BC=CE\). Let the lines \(CD\) and \(BE\) meet at \(F\). Prove that the incentre \(I\) of triangle \(ABC\), the orthocentre \(H\) of triangle \(DEF\) and the midpoint \(M\) of the arc \(BAC\) of the circumcircle of triangle \(ABC\) are collinear.

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Thinking Out Loud – EGMO 2013 Problem 1

EGMO 2013, problem 1. The side \(\textrm{BC}\) of the triangle \(\textrm{ABC}\) is extended beyond \(\textrm{C}\) to \(\textrm{D}\) so that \(\textrm{CD} = \textrm{BC}\). The side \(\textrm{CA}\) is extended beyond \(\textrm{A}\) to \(\textrm{E}\) so that \(\textrm{AE} = 2\textrm{CA}\). Prove that if \(\textrm{AD} = \textrm{BE}\), then the triangle \(\textrm{ABC}\) is right-angled.

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Thinking Out Loud – EGMO 2013 Problem 2

EGMO 2013, problem 2. Determine all integers \(m\) for which the \(m\times m\) square can be dissected into five rectangles, the side lengths of which are the integers \(1, 2, 3, \dotsc, 10\) in some order.

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Thinking Out Loud – EGMO 2013 Problem 3

EGMO 2013, problem 3. Let \(n\) be a positive integer.

  1. Prove that there exists a set \(S\) of \(6n\) pairwise different positive integers, such that the least common multiple of any two elements of \(S\) is no larger than \(32n^2\).
  2. Prove that every set \(T\) of \(6n\) pairwise different positive integers contains two elements the least common multiple of which is larger than \(9n^2\).

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