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The 7th Asian Pacific Mathematical Olympiad
1995年第7届亚太地区数学奥林匹克
  1. Determine all sequences of real numbers a1, a2, ... , a1995 which satisfy:
    2√( an -(n - 1) )≥ an+1 - (n - 1); for n = 1, 2, ... ,1994;
    and 2√(a1995 - 1994) ≥ a1 + 1.
  2. Let a1, a2, . . . , an be a sequence of integers with values between 2 and 1995 such that:
    (i) Any two of the ai’s are realtively prime,
    (ii) Each ai is either a prime or a product of primes.
    Determine the smallest possible values of n to make sure that the sequence will contain a
    prime number.
  3. Let PQRS be a cyclic quadrilateral such that the segments PQ and RS are not parallel.Consider the set of circles through P and Q, and the set of circles through R and S.Determine the set A of points of tangency of circles in these two sets.
  4. Let C be a circle with radius R and centre O, and S a fixed point in the interior of C. Let AA' and BB' be perpendicular chords through S. Consider the rectangles SAMB, SBN'A', SA'M'B', and SB'NA. Find the set of all points M, N', M', and N when A moves around the whole circle.
  5. Find the minimum positive integer k such that there exists a function f from the set Z of all integers to {1, 2, ..., k} with the property that f(x) ≠ f(y) whenever |x - y|∈{ 5, 7, 12 }.
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