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: Can some one explain why I am getting this wrong

  1. Aug 2, 2008 #1
    Can some one explain why I am getting this wrong[SOLVED]

    1. The problem statement, all variables and given/known data
    Evaluate
    [tex]\int ln(x+x^{2}) dx[/tex]

    2. Relevant equations



    3. The attempt at a solution
    I integrated by parts to get down to [tex]xln(x+x^{2})-\int \frac{(2x-1)}{x+1}[/tex] I set [tex] u=1+x[/tex] which led to [tex]du=1 dx[/tex] and [tex]x=u-1[/tex] after so evaluation I got down to [tex]-(\int 2 du -\int \frac{1}{u} du)[/tex] and after more substitution and evaluation I got down to [tex]xln(x+x^{2})+ln\left|1+x \right|-2-2x +C[/tex], but my book says that I should have only got -2x and not that extra -2
     
    Last edited: Aug 2, 2008
  2. jcsd
  3. Aug 2, 2008 #2
    Nevermind I figured it out
     
  4. Aug 2, 2008 #3
    Huh weird, this same problem was solved yesterday. Which book are you using for calculus if you don't mind me asking?
     
  5. Aug 2, 2008 #4
    Thomas Calculus, I still don't get how I messed up on substitution but I just long divided and got the answer
     
  6. Aug 2, 2008 #5

    rock.freak667

    User Avatar
    Homework Helper

    You didn't need to use integration by parts though.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook