The displacement of a progressive wave is represented by  where x is distance and t is time. Write the dimensional formula of (i) 
 and (ii) k.
According to the principle of homogeneity dimensional formula on L.H.S. & R.H.S. is equal.
Thus, the dimension of  = Dimension of y
 has no dimensions because it is an angle of sin.
Thus,  has no dimension & dimension of 
.