Soros:
\Large U = U_1 + U_2
\Large U_1 = I * R_1
\Large U_2 = I * R_2
\Large U = I(R_1 + R_2 )
\Large R_{eredo} = R_1 + R_2
Párhuzamos:
\Large I = I_1 + I_2
\Large U = I_1 * R_1
\Large U = I_2 * R_2
\Large I = U(\frac{1}{R_1} + \frac{1}{R_2})
\Large \frac{1}{R_{eredo}} = \frac{1}{R_1} + \frac{1}{R_2}