2 \pi f_{c} t+m_{2}(t) \sin 2 \pi f_{c} t \text { in time domain and frequency domain. } \text { (b) The signal } e_{1}(t)=2 s(t) \cos 2 \pi f_{c} t \text { in time and frequency response. } \text { (c) The signal } e_{2}(t)=2 s(t) \sin 2 \pi f_{c} t \text { in time and frequency response. } (d) The two recovered message signals in time domain.

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