A student writes four different expressions for the displacement `y` in a periodic motion . Which of the following can be correct?

Write expression for displacement vector.

A student writes four different expression for the displacement y in a period motion y = a sin"(2 pi r)/(T) y = a sin vt y = (a)/(t) sin"(t)/(a) y = (a )/(sqrt(2))[sin'(2 pi r)/(T)+ cos '(2 pi r)/(T)] where a is maximum displacement , x is the speed and T is the time period then dimensionally.

Which of the following is a periodic motion ?

Write down the expression of displacement current .