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: Integration homework problem help

  1. Feb 12, 2008 #1
    1. The problem statement, all variables and given/known data
    I have this equation:
    integrate: dN/(4-2N)


    2. Relevant equations



    3. The attempt at a solution
    I am understanding that the dN part just goes away and comes one on the top of the fraction. Then on the bottom, I am still left with 4-2N. I am simply saying that it is equal to ln|4-2N| .. however, I am told that it should be -1/2 ln(|4-2N|) . The -1/2 in front, is that coming from performing a chain rule? And if so, how do you get a chain rule out of this?
     
  2. jcsd
  3. Feb 12, 2008 #2

    rock.freak667

    User Avatar
    Homework Helper

    [tex]\int \frac{1}{4-2N} dN[/tex]

    Let u=4-2N (*) ;[itex]\frac{du}{dN}=-2 \Rightarrow dN=\frac{du}{-2}[/itex]


    [tex]\int \frac{1}{4-2N} dN \equiv \int \frac{-1}{2} \frac{1}{u} du[/tex]

    [tex]\frac{-1}{2}\int \frac{1}{u} du = \frac{-1}{2}lnu + Constant[/tex]


    and *
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook