signal
assume
$ x(t) = e^{-5t}u(t) + e^{-4(t-1)}u(t-3) $
answer
$ x(w) = \int_{-\infty}^{\infty}x(t)e^{-jwt}dt $
$ =\int_{-\infty}^{\infty}(e^{-5t}u(t) + e{-4(t-1)})e^{-jwt}dt $
$ =\int_{0}^{\infty}e^{-5t} e^{-jwt}dt + \int_{3}^{\infty}e^{-4(t-1)}e^{-jwt}dt $
