Đáp án:

a) \(\dfrac{{131}}{{15}}\Omega \)

b) \(\dfrac{{180}}{{131}}A\)

c) \(\dfrac{{672}}{{131}}V\)

Giải thích các bước giải:

a) Ta có:

\(\begin{array}{l}
{R_{12}} = \dfrac{{{R_1}{R_2}}}{{{R_1} + {R_2}}} = \dfrac{{8.7}}{{8 + 7}} = \dfrac{{56}}{{15}}\Omega \\
{R_{AB}} = {R_3} + {R_{12}} = 5 + \dfrac{{56}}{{15}} = \dfrac{{131}}{{15}}\Omega 
\end{array}\)

b) Ta có:

\(\begin{array}{l}
{I_3} = {I_{AB}} = \dfrac{U}{{{R_{AB}}}} = \dfrac{{12}}{{\dfrac{{131}}{{15}}}} = \dfrac{{180}}{{131}}A\\
{I_1} = \dfrac{{{R_2}}}{{{R_1} + {R_2}}}.{I_{AB}} = \dfrac{7}{{15}}.\dfrac{{180}}{{131}} = \dfrac{{84}}{{131}}A\\
{I_2} = {I_{AB}} - {I_1} = \dfrac{{96}}{{131}}A
\end{array}\)

c) Ta có:

\(\begin{array}{l}
{U_1} = {U_2} = {I_1}{R_1} = \dfrac{{84}}{{131}}.8 = \dfrac{{672}}{{131}}V\\
{U_3} = {U_{AB}} - {U_1} = \dfrac{{900}}{{131}}V
\end{array}\)