Resposta:
[tex] \frac{1}{r} = \frac{1}{4} + \frac{1}{6} + \frac{1}{12} \: \: \: \: \frac{1}{r} = \frac{6}{12} \: \: \: \: \: r = 2ohms[/tex]
[tex]4 + ( \frac{4}{3} ) + 4 = \frac{28}{3} ohms[/tex]
[tex]10 + 4 + 8 = 22ohms[/tex]
[tex]6 + \frac{10(2 + 3 + 5)}{ 10+ (2 + 3 + 5)} + 4 = 15ohms[/tex]
