# Transformation with a fraction

• May 15th 2013, 05:12 AM
johncassell
Transformation with a fraction
Hi all, I have the following formula

$-ctLoge = log(\frac{a-b}{a})$

and I have to get 't' as the subject so I thought I would divide the right hand side by -cLoge to get this

$t = \frac{log(\frac{a-b}{a})}{-cLoge}$

However, my textbook says the answer is

$t = \frac{-log(\frac{a-b}{a})}{cLoge}$

Could someone please explain why my method wasn't correct?

Thanks very much
John
• May 15th 2013, 05:30 AM
zhandele
Re: Transformation with a fraction
Aren't they the same?

$\frac{1}{-2}=\frac{-1}{2}$

BTW, while I understand you, I'm used to seeing $ln$ used for the natural log.
• May 15th 2013, 05:52 AM
johncassell
Re: Transformation with a fraction
Ahh yes, so they are - don't understand why the textbook didn't just do it the way its been teaching me so far, but at least I know I hadn't actually made a mistake.

The example I was doing was a demonstration of using both common logs vs natural logs - just hadn't got to the natural log part example yet.

thanks for your help, much appreciated.