# Homework Help: Rearranging logs

1. Feb 8, 2017

Please excuse my ignorance for posting this question, but I am confusing myself here. All I want to know is if I am rearranging this equation properly to find the value required...

Question

I want to rearrange the following equation to make F1 the subject.

Equations
m1-m2=-2.5log10(F1/F2)

My Thinking

So rearranging the above formula for F1 it becomes:

F1=10-(m1-m2)/2.5 x F2

When it comes to rearranging logs (one of the most straight forward and simple things, I know) I find myself easily confused.

Please don't tell me the correct arrangement if I am wrong, just a little guidance please.

2. Feb 8, 2017

### Staff: Mentor

That doesn't look right to me.

Start by moving the -2.5 to the LHS. Then you have log_10() on the RHS, so raise both sides to 10^() to get rid of the log term...

3. Feb 8, 2017

Thanks,

So basically raise everything to 10, get rid of the logs, rearrange, take everything to the 10√ ?

F1=-F2(m1-m2/2.5)

Or is that silly?

4. Feb 8, 2017

### Staff: Mentor

No, not close. Try showing each step that I mention in my first reply, and then continue with the algebra after that. Please show each step separately so we can check it.

5. Feb 8, 2017

OK, thanks....

So here goes:

m1-m2=-2.5log10(F1/F2)

-(m1-m2)/2.5=log10(F1/F2)

F1/F2=10-(m1-m2)/2.5

Is this right so far?

6. Feb 8, 2017

### Staff: Mentor

Yes!

7. Feb 8, 2017

so to finish it off it would be:

F1=(F2)(10-(m1-m2)/2.5)

?

8. Feb 8, 2017

Yes.

9. Feb 8, 2017