Biểu thức nào sau đây biểu diễn IDFT của dãy hữu hạn

$x\left(n\right)=\frac{1}{N}\sum {}_{k=0}^{N-1}\mathrm{Unsupported\; }X\left(k\right)W{}_N^{-kn}$

$x\left(n\right)=\sum {}_{n=0}^{N-1}\mathrm{Unsupported\; }X\left(k\right)W{}_N^{kn}$

$x\left(n\right)=\{\begin{array}{c}\frac{1}{N}\sum {}_{k=0}^{N-1}\mathrm{Unsupported\; }X\left(k\right)W{}_N^{-kn}\\ 0\le n\le N-1\\ 0\\ \text{k}\text{c}\text{ò}\text{n}\text{l}\text{a}\text{i}\end{array}$

$x\left(n\right)=\{\begin{array}{c}\sum {}_{n=0}^{N-1}\mathrm{Unsupported\; }X\left(k\right)W{}_N^{kn}\\ 0\le k\le N-1\\ 0\\ \text{k}\text{c}\text{ò}\text{n}\text{l}\text{a}\text{i}\end{array}$