[QUE/TH-02002] TH-PROBLEM

For a gas satisfying van de Waals equation
$$
\left(P+{a\over v^2}\right) (v-b) = R\theta
$$
show that the critical temperature $\theta_c$, critical pressure
$P_c$, and the critical volume are given by

$\theta_c =
{8a\over27Rb}~,~~P_c={a\over27b^2}~,~~v_c=3b\,.\,.$