A DSB-SC modulated signal is demodulated by applying it to a coherent detector. (a) Evaluate the effect of a frequency error !J. f in the local carrier frequency of the detector, measured with respect to the carrier frequency of the incoming DSB-SC signal. (b) For the case of a sinusoidal modulating wave, show that because of this frequency error, the demodulated signal exhibits beats at the error frequency. Illustrate your answer with a sketch of this demodulated signal.