Hi all, I've got a question regarding a price elasticity problem and a partial derivative. That's what's given for the exercise: So, first of all we calculate all the demand with the given information. Which is: And then we come to the actual problem. (4. b) ) How do they get the partial derivative here? I assume that they are using the quotient rule, right? I would be really glad for a step by step explanation. Thank you so much!