1. The problem statement, all variables and given/known data I'm trying to take the derivative of f(x) = 4 / sqrt(1 - x). Normally if I have trouble I just plug my problem into Wolfram Alpha, and it saves the day. 2. Relevant equations However, I don't know why it takes the derivative of 1 - x in the numerator after using the chain rule on 1 / sqrt(1 - x) here: http://www.wolframalpha.com/input/?i=4+/+sqrt(1-+x) 3. The attempt at a solution I'll say that I understand everything up until the aforementioned point in the problem.