1. The problem statement, all variables and given/known data Finding the partial derivative with respect to y, so del(f)/del(y) 2. Relevant equations exp(x+z) - that is e^(x+z) 3. The attempt at a solution I firstly thought this was just e^(x+z) but then i realised, shouldn't it be just 0? Since you're finding the partial derivative with respect to y, and since there's no y variable in there, wouldn't it be 0, ie treating the whole equation as a constant?