Given that the Fourier transform of u(t)\operatorname{e}^{-t} is \frac{1}{1+\mathrm{j}\omega} use the duality principle to deduce the transform of {\frac{1}{1+{jt}}}.
We know {{F(\omega)}}\ =\ {\frac{1}{1+\mathrm{j}\omega}} is the Fourier transform of \textstyle f(t)\;=\;u(t)\,\mathrm{e}^{-t}. Therefore 2\pi(u(-\omega)\operatorname{e}^{\omega}) is the Fourier transform of {\frac{1}{1+{{jt}}}}.