Explanation:
√a is defined only when a >= 0.
Therefore for √4x * √(x + 2) to be defined, both 4x and x + 2 must be non-negative.
When 4x >= 0, x >= 0.
When x + 2 >= 0, x >= -2.
x >= 0 and x >= -2, therefore we have x >= 0. (D)
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