1987 USAMO Problems/Problem 1
Problem
Find all solutions to , where m and n are non-zero integers.
Do it
Solution
Expanding both sides, Note that can be canceled and as , can be factored out. Writing this as a quadratic equation in : . The discriminant equals , which we want to be a perfect square. Miraculously, this factors as . This is square iff (if and only if) is square or . It can be checked that the only nonzero that work are . Finally, plugging this in and discarding extraneous roots gives all possible ordered pairs as .
See Also
1987 USAMO (Problems • Resources) | ||
Preceded by First Problem |
Followed by Problem 2 | |
1 • 2 • 3 • 4 • 5 | ||
All USAMO Problems and Solutions |
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