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IRL_ABooklet

Ireland number theory

Problem

Show that the only choice of integers that satisfies the equation is .
Solution
It suffices to consider non-negative . Assume that there is a non-trivial solution, i.e. at least one of the numbers is positive. We pick such a solution with minimal sum . Now, must be even since the other two terms are even, so we can write and divide the new equation across by to get As before, we conclude that is even and divide the new equation by to get As before, we conclude that is even and divide the new equation by to get This is our original equation with replaced by whose sum is half the original sum. This gives a contradiction so there are no solutions.

Techniques

Infinite descent / root flippingTechniques: modulo, size analysis, order analysis, inequalities