I am not certain what you want to plot.
Perhaps —
% sampling frequency (fs) is 6000 Hz
fs1 = 6000;
% I want to take 100 samples of the analog signals
nSamples = 100;
% attempt at axis definition
t1=0:1/fs1:100;
% analog input signals
x1 = (sin(2*pi*1000*t1).^2).*(cos(2*pi*1000*t1).^3);
y1 = (1/8) - (1/8)*cos(1*pi*2000*t1);
figure
plot(t1, [x1; y1])
grid
xlabel('t')
ylabel('Amplitude')
legend('x1','y1', 'Location','best')
xlim([0 0.01]) % Optional
I restricted the region of the x-axis to plot here to show detail.
.
