\textbf{117.} If $f(x) = \dfrac{1}{2}(x + \sqrt{x^2 + 4})$, then $f^{-1}(x) + f^{-1}\!\left(\dfrac{1}{x}\right)$ equals which of the following? \medskip (4) zero \hfill (3) $x^2 - 1$ \hfill (2) $\dfrac{2}{x}$ \hfill (1) $2x$ %% Page 5