1. The problem statement, all variables and given/known data Actually this is not a problem. This is about something i couldnt understand. 2. Relevant equations where wt equals θ 3. The attempt at a solution I can understand that x=r.cosθ it is obvious. But i cant understand why Vx=-V.sin(w.t) When i take a triangle from that circle i end up finding Vx equal to V.sin(w.t) . Where do we get that minus? Also how does he find the angle as 90+wt in that equation? I think it should be 90 - wt Note: I dont want the explanation with derivative.