1) R34 = R3 + R4 = 10 + 20 = 30 Ом
R234 = R2*R34/ ( R2 + R34) = 10*30 / (10 + 30) = 300/ 40 = 7,5 Ом
R общ = R1234 = R1 + R234 = 2,5 + 7,5 = 10 Ом
2)R23 = R2 + R3 = 3 + 7 = 10 Ом
R45 = R4 + R5 = 10 + 5 = 15 Ом
R2345 = R23*R45 / (R23 + R45) = 10*15 / (10 + 15) = 150 / 25 = 6 Ом
R общ = R1 + R2345 = 8 + 6 = 14 Ом
3) R12 = R1 + R2 = 1 + 2 = 3 Ом
R134 = R12* R3 / ( R12 + R3 )= 3*3 /(3 + 3) = 9/6 = 1,5 Ом
R45 = R4*R5 / (R4 + R5) = 8*3,64 / (8 + 3,64) = 2,5 Ом
R общ = R134 + R45 = 1,5 + 2,5 = 4 Ом
4) R23 = R2 + R3 = 10 + 26 = 36 Ом
1/Rобщ = 1/R1 + 1/R23 + 1/ R4 = 1/ 16 + 1/36 + 1/ 48 = 16 / 144 = 1/9
Rобщ = 9 Ом
Закон Ома ... ешкин кот....