The way you set your x vector and then multiply by 60, you have increments of 4*pi (60*(pi/15)). Since you evaulate the cosine of angles that are multiples of 4*pi, those answers are all equal to 1 of course,then you multiply each by two.
What are you actually trying to do? Do you want your frequency to be 60 Hz or 60 radians per sample?
I'll assume 60 radians/sample for the moment.
x = 0:0.001:2*pi;
y = 2*cos(60*x);
plot(x,y)
If you want 60 cycles per second
x = 0:0.001:2;
y = 2*cos(2*pi*60*x);
plot(x,y)
