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IMC 1996 Problem 8

Source: IMC 1996

March 4, 2021
trigonometry

Problem Statement

Let θ\theta be a positive real number. Show that if k∈Nk\in \mathbb{N} and both cosh⁡kθ\cosh k \theta and cosh⁡(k+1)θ\cosh(k+1) \theta are rational, then so is cosh⁡θ\cosh \theta.
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