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

%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

[Walter Roberson]

Do you want f1 + (f2/2) or do you want (f1+f2)/2 ? If you are looking for beat frequencies then you want (f1+f2)/2 and (f1-f2)/2

[Serena Simpson]

Making the increments smaller worked! Thanks for looking at my code!

Answer 1

[David Hill]

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);

[Walter Roberson]

Yes, smaller increments are important too. With 1/10 or 2/10 increment and frequencies that end in 10s, the result of the multiplication was always an integer multiple of 2*pi, and so you were not sampling at different points on the wave.

[Serena Simpson]

Thank you so much! It worked. My grade is saved <3