1965 IMO Problems/Problem 4
Revision as of 16:52, 16 July 2009 by Xantos C. Guin (talk | contribs)
Problem
Find all sets of four real numbers ,
,
,
such that the sum of any one and the product of the other three is equal to
.
Solution
Let be the product of the four real numbers.
Then, for we have:
.
Multiplying by yields:
where
.
If , then we have
which is a solution.
So assume that . WLOG, let at least two of
equal
, and
OR
.
Case I:
Then we have:
Which has no non-zero solutions for .
Case II: AND
Then we have:
AND
So, we have as the only non-zero solution, and thus,
and all permutations are solutions.
Case III: AND
Then we have:
AND
Thus, there are no non-zero solutions for in this case.
Therefore, the solutions are: ;
;
;
;
.