The Function $f ( x ) = x ^ { 2 } - 5$

Multiple Choice

The function $f ( x ) = x ^ { 2 } - 5$ is one-to-one on the domain $( x \leq 0 )$ .Find $f ^ { - 1 } ( x )$ .

A) $f ^ { - 1 } ( x ) = x ^ { 2 } + 5$
B) $f ^ { - 1 } ( x ) = \sqrt { x + 5 }$
C) $f ^ { - 1 } ( x ) = - \sqrt { x + 5 }$
D) $f ^ { - 1 } ( x ) = \frac { 1 } { x ^ { 2 } - 5 }$
E) $f ^ { - 1 } ( x ) = \sqrt { x - 5 }$