IMO Shortlist 1967 problem 4
Dodao/la:
arhiva2. travnja 2012. Prove the following statement: If

and

are real numbers whose quotient is irrational, then any real number

can be approximated arbitrarily well by the numbers of the form

integers, i.e. for every number

and every positive real number

two integers

and

can be found so that

holds.
%V0
Prove the following statement: If $r_1$ and $r_2$ are real numbers whose quotient is irrational, then any real number $x$ can be approximated arbitrarily well by the numbers of the form $\ z_{k_1,k_2} = k_1r_1 + k_2r_2$ integers, i.e. for every number $x$ and every positive real number $p$ two integers $k_1$ and $k_2$ can be found so that $|x - (k_1r_1 + k_2r_2)| < p$ holds.
Izvor: Međunarodna matematička olimpijada, shortlist 1967