% Fichier exo4.9.tex - Ch. Rolland/O Reilly France
\documentclass{article}
\usepackage[latin1]{inputenc}
\begin{document}
$$
C_p - C_v = T
  \left(\frac{\partial V}{\partial T}\right)_P
  \left(\frac{\partial P}{\partial T}\right)_V
$$
\end{document}
