The pulsed cosine signal shown in Figure is “on” for two cycles and then “off” for a perio...

The pulsed cosine signal shown in Figure is “on” for two cycles and then “off” for a period of time equivalent to 18 cycles of the cosine wave. The signal is periodic and the frequency of the cosine wave is 200π rad/s.

(a) Sketch the frequency spectrum for this signal.

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(b) How would the frequency spectrum change if the frequency of the cosine wave was doubled?

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(c) How would the frequency spectrum change if the “off” time was halved?