For Algebra questions, I think the easiest way is plug-in. Clearly see f(1/x) = (1/x) / ((1/x) +1) = 1/(x+1). Don't take time to convert 1/(x+1) to a formula in terms of f(x), just examine each answer.
Ans A: f(x) = x/(x+1) wrong
Ans B: -f(x) = -x/(x+1) Wrong
Ans C: 1/f(x) = (x+1)/x Wrong
Ans D: 1 - f(x) = 1 - x/(x+1) = 1/(x+1) CORRECT
Please +1 KUDO if my post helps. Thank you.
"Designing cars consumes you; it has a hold on your spirit which is incredibly powerful. It's not something you can do part time, you have do it with all your heart and soul or you're going to get it wrong."
Chris Bangle - Former BMV Chief of Design.