1. The problem statement, all variables and given/known data I really cannot seem to be able to follow the logic of how you would use the product rule when using 4 vector differential operator. ∂μ is the differential operator, Aμ is a scalar field and φ and φ* is it's complex conjugate scalar field. I have the answer, I'd just really like to know how to follow the logic of the answer. 2. Relevant equations ∂μ(Aμφφ*)=...? 3. The attempt at a solution Literally have no idea what I'm doing.