8. If $f : [ 1 , \infty )$ is given by $f ( x ) = x + 1 / x$ then $f - 1 ( x )$ equals :\\ (A) $( x + \sqrt { } ( x 2 - 4 ) ) / 2$\\ (B) $x / 1 + x 2$\\ (C) $( x - \sqrt { } ( x 2 - 4 ) ) / 2$\\ (D) $1 + \sqrt { } ( \times 2 - 4 )$\\