\frac{p_{m}}{2 ρ_{v}} = \frac{p}{ρ_{v} + 2 ρ_{v} - 2 ρ} = \frac{p}{3 ρ_{v} - 2 ρ}

${\frac{p_m}{2\rho_v} = \frac{p}{\rho_v + 2\rho_v - 2\rho} = \frac{p}{3\rho_v-2\rho}}$