"If it snows and we don't have school, then (x^3)<0 implies x is negative" (Assume x is a real number).
A statement of the form "If X then Y" where Y is true, is always true in classical logic. If the consequent of a conditional is true, then it matters neither what the antecedent is, nor whether there's any actual connection between them.
In this case, your "Y" expresses a mathematical truth, so we can take it as being a proposition that is always and necessarily true (although from a mathematical point of view, not a logical one). Therefore, your particular "If X then Y" is always true no matter what your X is. For instance "If pigs can fly then x^3 < 0 implies x < 0" is likewise true.
It's worth nothing that there are other systems of logic that do try to explicitly capture relevance and/or causal relationships. Your statement might not be evaluated as true in one of those systems.