Because saying "or" means that both situations can satisfy the meaning of the question, the final result can be one of them, so choose union.

② K > 0 is discussed at the beginning, and the intersection-1/2 < K < 3 is taken in the calculation.

③ After ③k > 0, the intersection is still taken when calculating k 3.

Because the discussion of k > 0 means that this is a prerequisite, and the subsequent solutions must be carried out under this prerequisite, so the intersection is finally ruled out.

Note that the intersection of these two situations refers to the intersection of your calculated conclusions and preconditions, that is, the intersection of "k > 0" and "-1/2 < k < 3" in case ②, and the intersection of "k > 0" and "k 3" in case ③. Be careful not to think it is "K".