A simple pendulum having length l is given a small angular displacement at time t = 0 and released. After time t, the linear displacement of the bob of the pendulum is given by
$ Periodic time T = 2 \pi { l \over g } = \omega = {2 \omega \over T } \Rightarrow \omega = { g \over l } $ $ Linear \,displacement x = a cos \omega t $