Problem:
Let be the set of all nonconstant monic polynomials with integer coefficients satisfying . If is an element of with minimal degree, compute the only possible value of .
Solution
Solution:
First, note that the polynomial has both and as roots. It suffices to check whether a polynomial of degree at most 3 belongs in . Suppose . We compute
so we get that
By resolving linear dependencies, it's clear that and . It follows that if is not the zero polynomial, it must be cubic. It is then clear that has minimal degree in , and thus .
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