This is written badly. What this says is that is . What you mean is "Find f''(x) where
Of course,So
Does that seem right?
so this is the same as for and is not defined for x= 0.
I would consider it simpler (and better) to say "If so and , if x< 0, so and . Of course, |x| is not differentiable at x= 0 so neither is and so f'' does not exist at x= 0".