a) [tex]R_{1}nt(R_{2}//R_{3})\Rightarrow R_{tđ}=R_{1}+\frac{R_{2}R_{3}}{R_{2}+R_{3}}=...[/tex]
b);c) [tex]I_{1}=I_{12}=I=\frac{U}{R_{tđ}}=...[/tex]
[tex]\Rightarrow U_{1}=I_{1}R_{1}=...[/tex]
[tex]\Rightarrow U_{2} =U_{3}=U_{23}=U-U_{1}=...[/tex]
[tex]\Rightarrow I_{2}=\frac{U_{2}}{R_{2}}=....;I_{3}=\frac{U_{3}}{R_{3}}=....[/tex]