dS=(drond*S/drond*T)*dT+(drond*S/drond*V)*d*V

donc drond*S/drond*T=(V/T)*(drond*rho/drond*T) et drond*S/drond*V=(rho+P)/T.

Comme drond^2*S/drond*T*drond*V=drond^2*S/drond*Vdrond*T, (1/T)*(drond*rho/drond*T)=-(rho+P)/T^2=d((rho+P)/T)/dT