Jackson's Subsets

Find the smallest value of $$n$$ for which the following statement is true:

"Given a set of $$n$$ distinct real numbers $$\{x_1,\ldots,x_n\}$$, there will always exist at least one pair of those numbers $$x_a$$ and $$x_b$$ that satisfy the inequality $$\left|\dfrac{x_a-x_b}{1+x_ax_b}\right|\leq\dfrac{1}{\sqrt{3}}.$$"

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