Giúp mình nhanh với ạ.Cảm ơn bạn rất nhiều

Bài 114: 

a) K mở, mạch gồm: (R1 // (R2 nt R3)) nt R4 nt R5

Ta có:

\(\begin{array}{l}
{R_{23}} = {R_2} + {R_3} = 6 + 6 = 12\Omega \\
{R_{123}} = \dfrac{{{R_1}.{R_{23}}}}{{{R_1} + {R_{23}}}} = \dfrac{{6.12}}{{6 + 12}} = 4\Omega \\
R = {R_{123}} + {R_4} + {R_5} = 4 + 2 + \dfrac{2}{3} = \dfrac{{20}}{3}\Omega \\
I = \dfrac{U}{R} = \dfrac{U}{{\dfrac{{20}}{3}}} = 0,15U\\
{I_2} = \dfrac{{{R_1}}}{{{R_1} + {R_{23}}}}.I = \dfrac{6}{{6 + 12}}.0,15U = 0,05U\\
{U_V} = U - {U_2} = U - {I_2}{R_2} = U - 0,05U.6\\
 \Rightarrow U = \dfrac{{120}}{7}V
\end{array}\)

b) Khi K đóng, mạch gồm: (R2 // (R1 nt (R3 // R4))) nt R5

Ta có:

\(\begin{array}{l}
{U_V} = 0V\\
{R_{34}} = \dfrac{{{R_3}{R_4}}}{{{R_3} + {R_4}}} = \dfrac{{6.2}}{{6 + 2}} = 1,5\Omega \\
{R_{134}} = {R_1} + {R_{34}} = 6 + 1,5 = 7,5\Omega \\
{R_{1234}} = \dfrac{{{R_2}.{R_{134}}}}{{{R_2} + {R_{134}}}} = \dfrac{{6.7,5}}{{6 + 7,5}} = \dfrac{{10}}{3}\Omega \\
R = {R_{1234}} + {R_5} = \dfrac{{10}}{3} + \dfrac{2}{3} = 4\Omega \\
I = \dfrac{U}{R} = \dfrac{{\dfrac{{120}}{7}}}{4} = \dfrac{{30}}{7}A\\
{I_5} = I = \dfrac{{30}}{7}A\\
{I_{134}} = \dfrac{{{R_2}}}{{{R_2} + {R_{134}}}}.I = \dfrac{6}{{6 + 7,5}}.\dfrac{{30}}{7} = \dfrac{{40}}{{21}}A\\
{I_4} = \dfrac{{{R_3}}}{{{R_3} + {R_4}}}.{I_{134}} = \dfrac{6}{{6 + 2}}.\dfrac{{40}}{{21}} = \dfrac{{10}}{7}A\\
{I_A} = {I_5} - {I_4} = \dfrac{{30}}{7} - \dfrac{{10}}{7} = \dfrac{{20}}{7}A
\end{array}\)

Bài 115:

Mạch gồm: R5 nt (R2 // ((R3 // R4) nt R1)) nt R6

Ta có:

\(\begin{array}{l}
{R_{34}} = \dfrac{{{R_3}{R_4}}}{{{R_3} + {R_4}}} = \dfrac{{2.8}}{{2 + 8}} = 1,6\Omega \\
{R_{134}} = {R_1} + {R_{34}} = 1,4 + 1,6 = 3\Omega \\
{R_{1234}} = \dfrac{{{R_2}{R_{134}}}}{{{R_2} + {R_{134}}}} = \dfrac{{6.3}}{{6 + 3}} = 2\Omega \\
R = {R_5} + {R_{1234}} + {R_6} = 6 + 2 + 2 = 10\Omega \\
I = \dfrac{U}{R} = \dfrac{9}{{10}} = 0,9A\\
{I_5} = I = 0,9A\\
{U_V} = U - {U_6} = U - {I_6}{R_6} = 9 - 0,6.2 = 7,8V\\
{I_{134}} = \dfrac{{{R_2}}}{{{R_2} + {R_{134}}}}.I = \dfrac{6}{{6 + 3}}.0,9 = 0,6A\\
{I_4} = \dfrac{{{R_3}}}{{{R_3} + {R_4}}}.{I_{134}} = \dfrac{2}{{2 + 8}}.0,6 = 0,12A\\
{I_A} = {I_5} - {I_4} = 0,9 - 0,12 = 0,78A
\end{array}\)