exam

clear
clc
f1 = 3e3
f2=27405e3
fs = 10*f2
t = [0 : 1/fs : 2/f1];
signal = 2*cos (2*pi*f1.*t).*cos(2*pi*f2.*t);
plot (t, signal);

Nsamps = length (signal)
fft_signal = abs (fft (signal));
fft_signal = fft_signal (1:Nsamps/2);
f_spec = fs*(0:Nsamps/2-1)/Nsamps;
plot (f_spec, fft_signal, 'linewidth', 1.5, '-r');
xlim ([0 5.6e7]);