The displecement-time equation of a particle executing `SHM` is `x = A sin (omega t + phi)` At time `t = 0` position of the position is `x = A//2` and it is moving along negative `x- direction` .Then the angle `phi` can be

Explanation

At `t=0,x=a//2, so (a)/(2)=asinphi or sinphi=(1)/(2)`
or `phi=(pi)/(6)` or `(5pi)/(6)`
Velocity, `v=(dx)/(dt)=aomegacos(omegat+phi)`
At `t=0, v=aomegacos phi,`
Here, `cos((pi)/(6))=(sqrt(3))/(2) ` and ` cos((5pi)/(6))=-(sqrt(3))/(2)`