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 ....

Therefore

I'm just not sure what's happening with the 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