[tex]a)R_{2,3}=\frac{R_2R_3}{R_2+R_3}=\frac{10*40}{10+40}=\frac{400}{50}=8\Omega\\ Re=R_1+R_{2,3}=10+8=18\Omega=>Re=18\Omega\\b)U_{AC}=U_{AB}+U_{BC}\\U_{BC}=I_1R_{2,3}\\U_{AB}=I_1R_1\\U_{AC}=U_{BC}+U_{AB}=I_1R_{2,3}+I_1R_1=I_1(R_1+R_{2,3})=>I_1=\frac{U_{AC}}{R_1+R_{2,3}}=\frac{9}{18}=0,5 A=>I_1=0,5 A\\c) U_{AB}=I_1R_1=0,5*10=5 V=>U_{AB}=5 V\\U_{AC}=U_{BC}+U_{AB}=>U_{BC}=U_{AC}-U_{AB}=9-5=4V=>U_{BC}=4V[/tex]
[tex]d) U_{BC}=I_2R_2=>I_2=\frac{U_{BC}}{R_2}=\frac{4}{10}=0,4 A=>I_2=0,4 A\\ U_{BC}=I_3R_3=>I_3=\frac{U_{BC}}{R_3}=\frac{4}{40}=0,1 A=>I_3=0,1 A\\ e) I_1=I_2+I_3<=>0,5=0,4+0,1<=>0,5=0,5(A)[/tex]
