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My reading of the problem is different from that of the tutor @MathLover1,
and my solution is different, too, as well as my answer.
If + = and x and y are positive integers, then what is the value of ?
Solution
+ = ====>
= - ====> square both sides ====>
x = - + . (*)
Since x and y in this equation are integers, must be integer.
Hence, the factor "y" must complement the number 45 to a perfect square.
It implies that y = 5.
Then from (*) x = = = 20.
Answer. If = and x and y are positive integers, then = = = 5.
Solved.
Nice solution to a nice problem.
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Specially for the tutor @MathLover1, I'd like to explain, why I think that my reading of the problem is correct.
We are given an info about the symmetric function f(x,y) = .
Therefore, the question should be (and, actually, MUST BE) about a symmetric function, too; in this case, about the function .