fs = 100;
t = [0:1/fs:1/fs * 10];
f1 = 80;
f2 = 20;
x1 = cos(2*pi*f1*t);
x2 = cos(2*pi*f2*t);

subplot(2,1,1);
plot(t,x1);
subplot(2,1,2);
plot(t,x2);