The difference between these equations for Dynamic Pitching?
 

I'm attempting to analyze a 2D airfoil in a pitching motion. However I have seen so many UDF defining the pitching motion like these...

/* define motion variables */
pitchampl = 45 * pi / 180; /* 45-degree pitch amplitude */
w = 2 * pi * 25; /* 25 Hz frequency */

/* define airfoil motion */
(1) omega[2] = w * pitchampl * cos(w * time);

(2) omega[2] = w * pitchampl * sin(w * time);

I have also seen this equation

(3) omega[2] = 0.5 * pitchampl * sin(w*time);

Please I need help with the difference between these equations(1,2 and 3), which is the correct one for pitching motion of airfoil ? Is it sin or cos ?

Thanks