Consider U = {x|x is a negative real number}.Which is an empty set?

A negative real number has a negative cube root, so choice A is not empty. But no real number has a square root that is negative: the real square root of a nonnegative number is nonnegative, and negative numbers have no real square roots. Thus no member of U satisfies choice B, making “x has a negative square root” the empty set.

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