Biết u AN = 150 cos(100pi t + pi/2)V, u MB = 50 căn 6cos(100pi t + pi/12)V cuộn dây thuần cảm.

Ta có:
\(U_{AN} = \sqrt{U^2_R + U_L^2} = 75\sqrt{2}\Rightarrow U_L = \sqrt{11250 -U_R^2}\)
\(\Rightarrow \varphi _{U_{AN}} - \varphi _i = arctan (\frac{U_L}{U_R}) = arctan(\frac{\sqrt{11250 - U_R^2}}{U_R})\)
\(U_{MB} = \sqrt{U_R^2 + U_C^2} = 50\sqrt{3}\Rightarrow U_C = \sqrt{7500 - U_R^2}\)
\(\Rightarrow \varphi _{U_{MB}} - \varphi _i = arctan (\frac{- U_C}{U_R}) = arctan(\frac{- \sqrt{7500 - U_R^2}}{U_R})\)
\(\Rightarrow \varphi _{U_{AN}} - \varphi _i - \varphi _{U_{MB}}- \varphi _i \Leftrightarrow arctan (\frac{\sqrt{11250 - U_R^2}}{U_R}) - arctan (\frac{-\sqrt{7500 - U_R^2}}{U_R}) = \frac{5 \pi}{12}\)
\(\Rightarrow U_R = 75 V \Rightarrow U_L = 75 \Rightarrow U_C = 25\sqrt{3}\)
Điện áp hai đầu \(U_{AB}:U_{AB} = \sqrt{U_R^2 + (U_L - U_C)^2} = 81,42 V\)