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: Intergration using logarithms

  1. Jan 13, 2008 #1
    Evaluate the integral.

    [tex]\int3/(3x-2) dx[/tex] from 0 to -1 (top to bottom).

    I change the equation to [tex(1/x - 3/2) dx[/tex]
    then integrated ln x-3/2x, but ln x at 0 is undefined.

    The text book shows it as becoming ln (3x-2), but I'm not completely understanding how to get to that.
  2. jcsd
  3. Jan 13, 2008 #2


    User Avatar
    Homework Helper

    substitute y = 3x-2
  4. Jan 13, 2008 #3
    Thanks, that worked. I'm just a bit rusty I reckon.
  5. Jan 14, 2008 #4


    User Avatar
    Science Advisor

    Caution: you are going to find it very difficult to do Calculus if you cannot do basic algebra.

    [itex]a/(b+c)[/itex] is not equal to (a/b)+ (a/c)!

    You had better review your algebra.
  6. Jan 14, 2008 #5
    Hmm, guess you're right. I've always used (a+b)/c=a/c+b/c but guess I just assumed it would work vice versa. Is there any combination it does equal?
  7. Jan 14, 2008 #6
    My 1st help in answering !!

    1- You have to use change of variables method.
    2- Substitute den with a variable and take derivative of this wrt x
    3- Using this var the limits will change
    4- Once you do 2 and with new limits from 3, the integral will be easy.


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