Given the following figures take m$($t$)=$cos$\backslash$omega $\_($m$)$t$,$k$\_($v$)=3,$f$\_($c$)=9$f$\_($m$),($f$\_($m$)=(\backslash$omega $\_($m$))/(2)\backslash$pi $)$

Fig. Q$\mathrm{.}4\mathrm{.}1.$ Modulator

Fig. Q$\mathrm{.}4\mathrm{.}2.$ Demodulator

Q$\mathrm{.}4\mathrm{.}1$ What kind of modulation is performed in Fig. Q$\mathrm{.}4\mathrm{.}1?($Be specific$)$

Q$\mathrm{.}4\mathrm{.}2$ What kind of demodulation is performed in Fig. Q$\mathrm{.}4\mathrm{.}2?($Be specific$)$

Q$\mathrm{.}4\mathrm{.}3$ Determine an expression for the signal r$($t$)$ in the time domain.

Q$\mathrm{.}4\mathrm{.}4$ Derive an expression for the frequency domain of the modulated signal R$($f$)$ and

draw the amplitude spectrum. Indicate all amplitudes and frequencies clearly on

the spectrum.