a) 1/Rz1= 1/R1+ 1/R2= 1/2+1/2=1
Rz1= 1
Rz= Rz1+R3= 1+2= 3 Om
b)
Rz1= R3+R4= 2+2=4
1/Rz2= 1/Rz1+ 1/R2= 1/4+1/2 = 1/4+2/4= 3/4 Om
Rz2= 4/3
Rz= Rz2+R1= 4/3+2 = 3 i 1/3 Om
c)
Rz1= R1+R3+R4= 2+2+2= 6
1/Rz=1/R2+ 1/Rz1 = 1/2 +1/6 = 3/6+1/6= 4/6
Rz= 6/4= 1 i 1/2 Om