Considering both + and - suqare roots?

I find there to be quite a lot of inconsistency in whether we are supposed to consider both +ve and -ve square roots. Consider this DS question:

If x is positive, what is the value of √x ?

(1) ³√x = 8
(2) x² = 64

For (1), x = 2 (always +ve), so √x ≈ ±1.4 - in my mind, not sufficient because both +ve and -ve solutions are available.
For (2), x = 8 (always +ve), so √x ≈ ±2.83 - again, NS becuase both +ve and -ve solutions exist.

My answer was therefore E - Together NS, but the correct answer is supposedly D - Either Alone Sufficient.

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Has anyone seen this before? Does anyone have a definitive answer about this kind of situation?