[tex]\displaystyle v_{med}=\frac{d}{t} \\ \\ d=d_1+d_2 \\ d_1=d_2=\frac{d}{2} \\ \\ t=t_1+t_2 \\ \\ t_1=\frac{d_1}{v_1}=\frac{\frac{d}{2}}{v_1}=\frac{d}{2v_1} \\ \\ t_2=\frac{d_2}{v_2}=\frac{\frac{d}{2}}{v_2}=\frac{d}{2v_2} \\ \\ v_{med}=\frac{d}{\frac{d}{2v_1}+\frac{d}{2v_2}} \\ \\ Dupa \ simplificari \ se \ obtine \\ \\ v_{med}=\frac{2v_1v_2}{v_1+v_2}=48km/h[/tex]
