Find all triples of integers such that
Solution
We replace by , for some odd prime. Subtracting the first equation from the second, we obtain
We have and , so precisely two of them are positive. Assume that and . Without loss of generality, suppose . Because is a prime, the only possibility is
Then , , and the first equation reduces to
The only solution is , implying and .
The solutions are , and . We have , hence the desired triples are , , and .
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