1)
[tex]R_0=\sum\limits_{i=1}^nR_i \Rightarrow R_0=R_1+R_2[/tex]

2)

[tex]I_0=\frac{U_0}{R_0} =\frac{\sum\limits_{i=1}^nU_i}{\sum\limits_{i=1}^nR_i}[/tex]

[tex]I_0=\frac{U_1+U_2}{R_1+R_2}[/tex]