Hãy xác định giá trị của tích phân ∫ − π π Unsupported  e j ω ( l − n ) d ω

$\int {}_{-\pi }^{\pi }\mathrm{Unsupported\; }e{}^{j\omega \left(l-n\right)}d\omega =\{\begin{array}{c}2\pi \\ l=n\\ 0\\ l\ne n\end{array}$

${{\displaystyle \int }}^{\pi }\mathrm{Unsupported\; }e{}^{j\omega \left(l-n\right)}d\omega =\{\begin{array}{c}0\\ l=n\\ 2\pi \\ l\ne n\end{array}$

$\int {}_{-\pi }^{\pi }\mathrm{Unsupported\; }e{}^{j\omega \left(l-n\right)}d\omega =0$

${{\displaystyle \int }}^{\pi }\mathrm{Unsupported\; }e{}^{j\omega \left(l-n\right)}d\omega =2\pi$