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【单选题】
“xy<0”是“x<0且y>0”的( )A.
充分不必要条件
B.
充要条件
C.
既不充分也不必要条件
D.
必要不充分条件
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举一反三
【单选题】无源二端网络如图所示。输入端的电压 u=220 cos ( 314t+20 ̊ ) V , 电流 i=220 cos ( 314t - 33 ̊ ) A ,试求此二端网络的由两个元件串联的等效电路的功率因数 cosφ= ,该网络的性质为 。
A.
0.6，容性
B.
0.8，容性
C.
0.6，感性
D.
0.8，感性
【单选题】听力原文：M: It's such a nice warm day. I think I'll go and write my report under the oak tree. W: I'd like to join you but I find it hard to concentrate outside, and I need to finish my paper this afterno...
A.
Go and read under the oak tree with the man.
B.
Go and write the report with the man.
C.
Stay at home and finish writing her report.
D.
Stay at home and finish writing her paper.
【单选题】听力原文：M: It's such a nice warm day. I think I'll go and write my report under the oak tree. W: I'd like to join you but I find it hard to concentrate outside, and I need to finish my paper this afterno...
A.
Go and read under the oak tree with the man.
B.
Go and write the report with the man.
C.
Stay at home and finish writing her report.
D.
Stay at home and finish writing her paper.
【简答题】无源二端网络如图所示。输入端的电压 u=220 cos ( 314t+20 ̊ ) V , 电流 i=220 cos ( 314t - 33 ̊ ) A ,试求此二端网络的由两个元件串联的等效电路的功率因数 cosφ= ,该网络的性质为 。
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