Tìm X ( e j ω ) biết x ( n ) = a n ⋅ r e c t N ( n )

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

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

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

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