Your expression misses the second term above.
By the way for the first equality your wrote it's just the chain rule, Chain rule - Wikipedia, the free encyclopedia
Hey, hope someone will help me
I need some help to rewrite a differential equation.
I start with the expression :
This reason why this apply (correct me if I'm wrong) is this:
Furthermore this applies:
This I can't explain, if someone could explain to me why and how (detailed if possible), it would be great.
Sorry if it is obvius, but I'm new to this.