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Accoring to your equations, either re (Zin) must be negative (impossible for a passive circuit) or L would be negative, too. Apart from that, the Q equation would be valid only for a pure RL circuit, which is always in doubt for an inductor considering an extended frequency range.
Perhaps you should go back to the original definition of the quality factor: Q=1/tanδ.
The angle δ is simply the angle between voltage and current of the inductor (which is zero for a lossless inductor)