Hello, this is my first post on this forum and it is about simple harmonic motion. I can't seem to understand why the displacement x has two functions. What I mean is, x(t)=A.Sin(wt+phi) is the solution of differential equation of s.h.m; which is used by our physics teacher to derive the velocity and acceleration of a particle performing s.h.m; BUT in many text books I found that x(t)=A.Cos(wt+phi) ... my question is how can there be two values for x ? Any help would be very helpfull, Thank You. Rohit Arondekar.