# Straightforward differentiation, but think I have wrong sign somewhere

1. Feb 18, 2009

### phyzmatix

1. The problem statement, all variables and given/known data, attempt at a solution

Please see attached. I'm actually busy with a physics problem, but solving it requires that I complete this part correctly. It's straightforward differentiation, but I think I made an error with my signs somewhere and I can't for the life of me find where...

Any pointers? (I believe this is going to be one of those *doh* situations )
phyz

#### Attached Files:

• ###### Question and Attempted Solution.pdf
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2. Feb 18, 2009

### Tom Mattson

Staff Emeritus
There's nothing wrong. The quantity in brackets in the last line is in fact zero. Don't forget:

$$x\cdot x^{-7/2}=x^{1-7/2}=x^{-5/2}$$

3. Feb 18, 2009

### phyzmatix

You see...*DOH!*

Thanks for the help!