A.\(u = 80\sqrt 2 .cos\left( {100\pi t - \frac{\pi }{3}} \right)V\)
B.\(u = 80.cos\left( {100\pi t - \frac{\pi }{3}} \right)V\)
C.\(u = 80\sqrt 2 .cos\left( {100\pi t + \frac{\pi }{3}} \right)V\)
D.\(u = 80.cos\left( {100\pi t + \frac{{2\pi }}{3}} \right)V\)