
Given, the instantaneous equation of motion of the particle is
x=Asin(ωt+δ)...(1)
As the particle is moving along positive x-axis, v=dtdx>0.
Substitute 0 for t and 2A for x into equation (1) and solve to calculate the required phase difference.
2A=⇒=⇒Asin(ω×0+δ)sinδ=21sin6πδ=6π