Hello!

Now, I have to count derivative from :

it would of course not be a problem IF the result would not be:

So, obviously it is the whole procedure including the proof of the rule for the derivative of the rational function and that is what I am asking about.

(Of course I am avare h is almost 0, but I am interested to the whoel procedure how didi they get it!)

I tried like this:

and got of course:

can someone help?

Did I make a mistake?

Many thanks!