Cho h ( n ) = a n ⋅ u ( n ) , xác định H ( e j w ) .

$H\left(e{}^{i\omega }\right)=\frac{1}{1-ae{}^{j\omega }}$

$H\left(e{}^{j\omega }\right)=-\frac{1}{1-ae{}^{-j\omega }}$

$H\left(e{}^{j\omega }\right)=\frac{1}{1+ae{}^{-j\omega }}$

$H\left(e{}^{j\omega }\right)=-\frac{1}{1+ae{}^{-j\omega }}$