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n is periodic with the smallest period 1995

Source: Vietnam TST 1995, Problem 6

July 27, 2008
functionalgebra unsolvedalgebra

Problem Statement

Consider the function f(x) \equal{} \frac {2x^3 \minus{} 3}{3x^2 \minus{} 1}. 1. 1. Prove that there is a continuous function g(x) g(x) on R \mathbb{R} satisfying f(g(x)) \equal{} x and g(x)>x g(x) > x for all real x x. 2. 2. Show that there exists a real number a>1 a > 1 such that the sequence {an} \{a_n\}, n \equal{} 1, 2, \ldots, defined as follows a_0 \equal{} a, a_{n \plus{} 1} \equal{} f(a_n), nN \forall n\in\mathbb{N} is periodic with the smallest period 1995 1995.