Tìm X ( e j ω ) biết x ( n ) = 1 với 0 ≤ n < 2

$X\left(e{}^{j\omega }\right)=1+e{}^{j\omega }+e{}^{j2\omega }$

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

$X\left(e{}^{j\omega }\right)=1+e{}^{j\omega }$

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