【单选题】某正弦电压的最大值为311V,周期为0.02s、初相为30°,则该正弦电压的表达式为
【简答题】已知:a,b,c都是正实数,且ab+bc+ca=1.求证: .
【单选题】What is an advantage of an externally modulated laser over a directly modulated laser?()
D.
higher dispersion tolerance
E.
higher optical signal-to-noise ratio
【判断题】The envelope of the AM signal can fully reflect the information of the modulated signal when the AM Ma is less than 1. ( )