18. 19. 20. Show that any system that obeys the energy relationship U(T) = CT + Uo, where C and Uo are constants, must have an entropy expression of the form S(U) = C In(U - Uo) + So. Show that any system that obeys the pressure relationship P(V,T) = a, where a is a constant, must have an entropy expression of the form S(V) = a ln(V) + So. Starting from the definitions ofte