1. The problem statement, all variables and given/known data First law can be written dU = TdS - PdV where the internal energy U may be written in terms of any two of T,P,V,S. I have to show that (DT/DV)s = -(DP/DS)v where D is partial d, and the subscripts s and v mean hold those constant.. 2. Relevant equations 3. The attempt at a solution Not really sure how to proceed at all?