A little bit of help rearranging and equation

  • Thread starter SMOF
  • Start date
  • #1
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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
 

Answers and Replies

  • #2
gb7nash
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In order to apply the log, you need to isolate the e(-x2/4Dt) term. How do you do that?
 
  • #3
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Hello.

Well, that would be

CB/Co = e(-x2/Dt)
 
  • #4
gb7nash
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Ok, now log both sides. What do you get?
 
  • #5
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See, this is where im not sure.

Is it

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

?
 
  • #6
gb7nash
Homework Helper
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See, this is where im not sure.

Is it

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

?
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?
 
  • #7
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So,

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

?
 
  • #8
gb7nash
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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?
 
  • #9
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Well, that would be

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

and ln(e) is 1?
 
  • #10
gb7nash
Homework Helper
805
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Well, that would be

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

and ln(e) is 1?
Correct. You can probably take it from here.
 
  • #11
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Yea, thats fantastic!

Many thanks!

Seán
 

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