Good morning all, I am following a book which covers aspects of astronomy/cosmology, I'd like to know how the part in the middle is worked out. I have the start and end of the derivation but its quite scant on how it proceeds from point to point, the book simply says using the chain rule "this" becomes "this", basically.
Where the solution for is:
The result is:
This is simply for myself and trying to understand how the calculations are derived.
Thanks in advance