IMO Shortlist 1965 problem 4
Find all sets of four real numbers

such that the sum of any one and the product of the other three is equal to 2.
%V0
Find all sets of four real numbers $x_1, x_2, x_3, x_4$ such that the sum of any one and the product of the other three is equal to 2.
Source: Međunarodna matematička olimpijada, shortlist 1965