A. u(t)= 220cos(314t+30°)V B. u(t)=380sin(314t+30°)V C. u(t)=311cos(314t+30°)V D. u(t)=311cos(50t+30°)V
A. 有效值 B. 最大值 C. 瞬时值 D. 峰峰值
A. 对 B. 错