Let $f ( x , y , z ) = ( \sqrt { x y z } + \sqrt { - 2 z } + \sqrt { x - z } ) .$

Short Answer

Let $f ( x , y , z ) = ( \sqrt { x y z } + \sqrt { - 2 z } + \sqrt { x - z } ) .$ Compute f(1, -2, -1).
Enter your answer as a $\sqrt { b }$ .