Differentiation
x(t) = $ \int\limits_{-\infty}^{\infty}X(jw)e^{(-\jmath wt)}dt $
diffrentiate both sides
x'(t) = d($ \int\limits_{-\infty}^{\infty}X(jw)e^{(-\jmath wt)}dt $)
x'(t) = j*w*(j*w)
importance
replacing a differentiation operation in the time domain with a multiplication operation in the frequecy domain.
