1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Integral problem

  1. Jan 7, 2012 #1
    1. The problem statement, all variables and given/known data

    (ignore what's written, it isn't important for the problem)

    I'm studying integrals and I came across this solved example. However I can't understand where the minus of the integral came from came from.

    2. Relevant equations

    3. The attempt at a solution

    The primitive of a f^p * f ' function is f^(p+1) / (p+1) Therefore it should be ln^2(x-1)/2 and not -ln^2(x-1)/2

  2. jcsd
  3. Jan 7, 2012 #2
    You could dispel any doubts by making a u-substitution. Try [itex]u = 1 - x[/itex] and see where that takes you.
  4. Jan 7, 2012 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    By the chain rule: [itex]\displaystyle \frac{d}{dx}\ln(1-x)=\frac{1}{1-x}\frac{d}{dx}(1-x)=-\frac{1}{1-x}\,.[/itex]

    So you have the anti-derivative of f^p * (- f ' ) .
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook