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+//Example 2.3 page 24
+//Given an analog signal
+//x(t) = 5 cos (2 pi 2000t)+ 1 cos( 2pi 5000t), for t>=0
+//which is sampled at a rate of 8,000 Hz,
+//a. Sketch the spectrum of the sampled signal up to 20 kHz.
+//b. Sketch the recovered analog signal spectrum if an ideal lowpass filter with
+//a cutoff frequency of 4 kHz is used to recover the original signal
+//(y(n)= x(n) this case).
+
+clc,clear,close;
+
+c1 = [0.5 2.5 2.5 0.5];
+//sampling theorem is violated
+f1 = [-3 -2 2 3];//kHz
+
+//after sampling
+c2 = repmat(c1,1,5);
+f2 = [f1-16 f1-8 f1 f1+8 f1+16];
+ax=gda();
+ax.thickness = 2;
+ax.y_location = "origin";
+ax.x_location = "origin";
+
+subplot(2,1,1)
+plot2d3(f2,c2)
+xtitle('Spectrum of the sampled signal in Example 2.3(a)','f(kHz)','X(f)');
+//Since Sampling theorem is not satisfied, we can not recover the original spectrum using reconstruction low pass filter.
+subplot(2,1,2)
+plot2d3(f1,c1)
+xtitle('Spectrum of the recovered signal in Example 2.3(b)','f(kHz)','X(f)');