Giúp mik mn ơi

1) Khi K mở $\displaystyle C_{1} ntC_{2} ntC_{3}$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
a) \ C_{AB} =\frac{C_{1} C_{2} C_{3}}{C_{1} C_{2} +C_{2} C_{3} +C_{1} C_{3}} =\frac{1.1.1}{1.1+1.1+1.1} =\frac{1}{3} \mu F\\
b) \ Q_{1} =Q_{2} =Q_{3} =Q_{AB} =U_{AB} .C_{AB} =12.\frac{1}{3} .10^{-6} =4.10^{-6} C\\
Vì\ C_{1} =C_{2} =C_{3}\\
Nên\ U_{1} =U_{2} =U_{3} =\frac{Q_{1}}{C_{1}} =\frac{4.10^{-6}}{1.10^{-6}} =4V
\end{array}$

2) Khi K đóng: $\displaystyle C_{1} \ nt(( C_{2} ntC_{3}) //C_{4})$

$\displaystyle  \begin{array}{{>{\displaystyle}l}}
a) \ C_{23} =\frac{C_{2} C_{3}}{C_{2} +C_{3}} =\frac{1}{2} \mu F\\
C_{234} =C_{23} +C_{4} =\frac{1}{2} +2=2,5\mu F\\
C_{AB} =\frac{C_{1} .C_{234}}{C_{1} +C_{234}} =\frac{1.2,5}{1+2,5} =\frac{5}{7} \mu F\\
b) Q_{1} =Q_{234} =Q_{AB} =C_{AB} .U_{AB} =\frac{5}{7} .10^{-6} .12=\frac{60}{7} .10^{-6} C\\
U_{1} =\frac{Q_{1}}{C_{1}} =\frac{60}{7} V\\
U_{23} =U_{4} =U_{234} =U-U_{1} =\frac{24}{7} V\\
Q_{4} =C_{4} U_{4} =\frac{48}{7} .10^{-6} C\\
Q_{2} =Q_{3} =Q_{23} =C_{23} .U_{23} =\frac{1.1}{1+1} .10^{-6} .\frac{24}{7} =\frac{12}{7} .10^{-6} C\\
Vì\ C_{2} =C_{3}\rightarrow U_{2} =U_{3} =\frac{Q_{2}}{C_{2}} =\frac{\frac{12}{7} .10^{-6}}{10^{-6}} =\frac{12}{7} V
\end{array}$