X= Acos(wt)?? X= Asin(wt)?? 1. The problem statement, all variables and given/known data X= Acos(wt)?? X= Asin(wt)?? Which is right? in some books, x = A sin(wt), while in other books, x= Acos(wt)... I'm confused. Please explain this to me. Thank you very much.