Hãy xác định X ( k ) vói x ( n ) { a n 0 ≤ n ≤ N − 1 0 n   c o n   l a i  

$X\left(k\right)=\frac{1-a{}^N}{1-aW{}_N^k}$

$X\left(k\right)=\frac{1-a{}^{N}W{}_N^k}{1-W{}_N^{-kn}}$

$X\left(k\right)=\frac{1-a{}^N}{1-aW{}_N^{-kn}}$

$X\left(k\right)=\frac{1-a{}^{N}W{}_N^{-kn}}{1-aW{}_N^{-kn}}$