MATLAB: My cos function appears as a straight line instead of as a wave

plot

%Defining given varibles
t = 0 :.1 :3;
f1 = 130;
f2 = 120;
y1 = cosd(2*pi*f1*t);
y2 = cosd(2*pi*f2*t);
%% Section 2: Processing
%equation given
y = 2 .* cos(2.*pi.*(f1+f2./2).*t) .* cos(2.*pi.*(f1-f2./2).*t); %This is my function for the sound waves, however, it appears as a stright line

Best Answer

f1 = 130;
f2 = 120;
t=0:.001:3;%need smaller incrementing
y = 2*cos(2*pi*(f1+f2/2)*t).*cos(2*pi*(f1-f2/2)*t);
plot(t,y);