MathDB
IMO LongList 1967, The Democratic Republic Of Germany 4

Source: IMO LongList 1967, The Democratic Republic Of Germany 4

December 16, 2004
number theoryapproximationirrational number

Problem Statement

Prove the following statement: If r1r_1 and r2r_2 are real numbers whose quotient is irrational, then any real number xx can be approximated arbitrarily well by the numbers of the form  zk1,k2=k1r1+k2r2\ z_{k_1,k_2} = k_1r_1 + k_2r_2 integers, i.e. for every number xx and every positive real number pp two integers k1k_1 and k2k_2 can be found so that x(k1r1+k2r2)<p|x - (k_1r_1 + k_2r_2)| < p holds.