MathDB
Recursively defined function

Source: IMO Shortlist 1994, A5

August 10, 2008
functioninductionalgebrafunctional equationIMO Shortlist

Problem Statement

Let f(x) \equal{} \frac{x^2\plus{}1}{2x} for x0. x \neq 0. Define f^{(0)}(x) \equal{} x and f^{(n)}(x) \equal{} f(f^{(n\minus{}1)}(x)) for all positive integers n n and x0. x \neq 0. Prove that for all non-negative integers n n and x \neq \{\minus{}1,0,1\} \frac{f^{(n)}(x)}{f^{(n\plus{}1)}(x)} \equal{} 1 \plus{} \frac{1}{f \left( \left( \frac{x\plus{}1}{x\minus{}1} \right)^{2n} \right)}.