a)
\(\varphi = {\varphi _u} - {\varphi _i} = 0 - ( - \dfrac{\pi }{6}) = \dfrac{\pi }{6} > 0\\ \Rightarrow {\varphi _u} > {\varphi _i}\)
\(i\) trễ pha hơn \(u\)
b)
\(\varphi = {\varphi _u} - {\varphi _i} = 0 - \dfrac{\pi }{4} = - \dfrac{\pi }{4} < 0 \\\Rightarrow {\varphi _u} < {\varphi _i}\)
\(i\) nhanh pha hơn \(u\)
c)
\(\begin{array}{l}{i_3} = - 5\sqrt 2 {\rm{cos(}}100\pi t - \dfrac{{5\pi }}{6})\\ = 5\sqrt 2 {\rm{cos(}}100\pi t - \dfrac{{5\pi }}{6} + \pi )\\ = 5\sqrt 2 {\rm{cos(}}100\pi t + \dfrac{\pi }{6})(A)\end{array}\) \(\varphi = {\varphi _u} - {\varphi _i} = 0 - \dfrac{\pi }{6} = - \dfrac{\pi }{6} < 0\\\Rightarrow {\varphi _u} < {\varphi _i}\)
\(i\) nhanh pha hơn \(u\)
