1. The problem statement, all variables and given/known data A wave moving in the positive Ox-direction has displacement of particle of 0 at the origin, O at time = 0.The displacement-distance graph showed a positive sine graph. Write an expression for the variation of the displacement y with time t for the particle at O. 2. Relevant equations 3. The attempt at a solution My book said that for the particle at O, the equation of motion of particle is y= A sin (ωt). But shouldn't it be y= -A sin (ωt -kx) and when x=0, the equation became y=-A sin(ωt) since the particle at O must move down for the wave to propagate to the right hand side. And if its y= A sin (ωt - kx), at t=0 and the x=λ/4, then displacement is negative. This is inconsistent with the positive sine graph of displacement-distance graph. Someone please lend me a hand on this, Thanks alot.