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 The 22nd United States of America Mathematics Olympiad 1993年第22届美国数学奥林匹克 n > 1, and a and b are positive real numbers such that an - a - 1 = 0 and b2n - b - 3a = 0. Which is larger ? The diagonals of a convex quadrilateral meet at right angles at X. Show that the four points obtained by reflecting X in each of the sides are cyclic . Let S be the set of functions f defined on reals in the closed interval [0, 1] with non-negative real values such that f(1) = 1 and f(x) + f(y) ≤ f(x + y) for all x, y such that x + y ≤ 1. What is the smallest k such that f(x) ≤ kx for all f in S and all x ? The sequence an of odd positive integers is defined as follows: a1 = r, a2 = s, and an is the greatest odd divisor of an-1 + an-2. Show that, for sufficiently large n, an is constant and find this constant (in terms of r and s) . A sequence xn of positive reals satisfies xn-1xn+1 ≤ xn2. Let an be the average of the terms x0, x1, ... , xn and bn be the average of the terms x1, x2, ... , xn. Show that anbn-1 ≥ an-1bn . 点击此处查看相关视频讲解 在方框内输入单词或词组