1. Not finding help here? Sign up for a free 30min 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!

A little bit of help rearranging and equation

  1. Nov 11, 2011 #1
    Hello,

    Hopefully someone can help me rearrange this equation for x2.

    The equation is

    CB = Co e(-x2/4Dt)

    It is changing the e into a log that is throwing me.

    Thanks.

    Seán
     
  2. jcsd
  3. Nov 11, 2011 #2

    gb7nash

    User Avatar
    Homework Helper

    In order to apply the log, you need to isolate the e(-x2/4Dt) term. How do you do that?
     
  4. Nov 11, 2011 #3
    Hello.

    Well, that would be

    CB/Co = e(-x2/Dt)
     
  5. Nov 11, 2011 #4

    gb7nash

    User Avatar
    Homework Helper

    Ok, now log both sides. What do you get?
     
  6. Nov 11, 2011 #5
    See, this is where im not sure.

    Is it

    ln(CB/Co) = ln(-x2/Dt)

    ?
     
  7. Nov 11, 2011 #6

    gb7nash

    User Avatar
    Homework Helper

    The right-hand side is wrong. The left-hand side is fine. Take the ln of the right side, without trying to cancel anything out for now. What do we have?
     
  8. Nov 11, 2011 #7
    So,

    ln(CB/Co) = ln(e(-x2/Dt))

    ?
     
  9. Nov 11, 2011 #8

    gb7nash

    User Avatar
    Homework Helper

    That's fine. One well-known rule of ln is:

    ln(ab) = b ln(a)

    How can we apply this to the right-hand side?
     
  10. Nov 11, 2011 #9
    Well, that would be

    ln(CB/Co) = (-x2/Dt)ln(e)

    and ln(e) is 1?
     
  11. Nov 11, 2011 #10

    gb7nash

    User Avatar
    Homework Helper

    Correct. You can probably take it from here.
     
  12. Nov 11, 2011 #11
    Yea, thats fantastic!

    Many thanks!

    Seán
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: A little bit of help rearranging and equation
Loading...