Originally Posted by

**Rai** Hi guys, wonder if any of you can help me clarify something. Got a deadline coming up and have been asked to explain an equation I've used in my work ... I've got a derivation from the source I got the equation from, but I don't understand one of the steps ... here goes ....

$\displaystyle m\pm \sigma_m = constant - 2.5\log(S\pm N)$

$\displaystyle m\pm \sigma_m = constant - 2.5\log\left[S\left(1\pm \frac{N}{S}\right)\right]$

$\displaystyle m\pm \sigma_m = constant - 2.5\log S - 2.5\log\left(1+ \frac{N}{S}\right)$

Therefore

$\displaystyle \sigma_m = \pm 2.5\log \left(1 + \frac{1}{S/N}\right)$

I'm just not sure what's happening with the $\displaystyle \pm$ disappearing, changing places etc, so if anyone could show me how you get from line 2 to 3 and 3 to 4 I'd be very grateful!

Cheers,

Rai