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periodic function with certain periods

Source: China second round 2008 p2

March 3, 2012
functionalgebra unsolvedalgebra

Problem Statement

Let f(x)f(x) be a periodic function with periods TT and 11(0<T<10<T<1).Prove that: (1)If TT is rational,then there exists a prime pp such that 1p\frac{1}{p} is also a period of ff; (2)If TT is irrational,then there exists a strictly decreasing infinite sequence {ana_n},with 1>an>01>a_n>0 for all positive integer nn,such that all ana_n are periods of ff.