Sampling Theorem Using Matlab with Waveforms

clc;
clear all;
close all;
t=-10:0.01:10;
T=4;
fm=1/T;
x=cos(2*pi*fm*t);
subplot(2,2,1);
plot(t,x);
title('msg signal');
xlabel('time');
ylabel('amplitude');
fs1=1.6*fm;
fs2=2*fm;
fs3=8*fm;
%sampling with fs<2fm
n1=-4:1:4;
x1=cos(2*pi*fm/fs1*n1);
subplot(2,2,2);
stem(n1,x1);
hold on;
subplot(2,2,2);
plot(n1,x1,'r');
title('sampling when fs<2fm ');
xlabel('sample');
ylabel('amplitude');
%sampling with fs=2fm
n2=-5:1:5;
x2=cos(2*pi*fm/fs2*n2);
subplot(2,2,3);
stem(n2,x2);
hold on;
subplot(2,2,3);
plot(n2,x2,'r');
title('sampling when fs=2fm ');
xlabel('sample');
ylabel('amplitude');
%sampling with fs>2fm
n3=-20:1:20;
x3=cos(2*pi*fm/fs3*n3);
subplot(2,2,4);
stem(n3,x3);
hold on;
subplot(2,2,4);
plot(n3,x3,'r');
title('sampling when fs>2fm ');
xlabel('sample');
ylabel('amplitude');