1. The problem statement, all variables and given/known data Hi, i have a little problem with a demostration, I hope you can help me. 2. Relevant equations this said that we have a system, a gas is containing in a recipe, there's no heat exchange neither work with the enviroment, only an expansion v to 2v, we have to find that (dT/dv)u=-(T^2/Cv)(d/dT)(P/T)v 3. The attempt at a solution I start with dU=(dU/dT)vdT+(dU/dv)t dU=0 (dT/dv)u=-(dU/dv)(dT/dU)vdv (dT/du)v=1/Cv (dT/du)=-(1/cv)(T(dP/dT)-P) I don't know how continue!