提示计算相量的相位角时要注意所在象限 ∪=3+j4 今=5√2co(at+531 j4→l=5√2cos(0t-531) U=-3+4→=5√2cs(0t+1269 U=-3-14=l=5√2cos(t-1269提示 计算相量的相位角时要注意所在象限 U = −3+ j4  U = 3+ j4  5 2 cos( 53 1 )  u =  t +  U = 3− j4  5 2 cos( 53 1 )  u =  t −  5 2 cos( 126 9 )  u =  t +  U = −3− j4  5 2 cos( 126 9 )  u =  t − 