Biểu thức nào sau đây biểu diễn IDFT của dãy X ˜ ( k )

$\tilde{x}\left(n\right)=\frac{1}{N}{\displaystyle \sum }_{k=-\infty }\mathrm{Unsupported\; }\tilde{X}\left(k\right)\cdot \text{W}{}_{\text{N}}^{-\text{k}\text{n}}$

$\tilde{x}\left(n\right)={\displaystyle \sum }_{k=0}\mathrm{Unsupported\; }\tilde{X}\left(k\right)\cdot \text{W}{}_{\text{N}}^{\text{k}\text{n}}$

$\tilde{x}\left(n\right)={\displaystyle \sum }_{k=0}\mathrm{Unsupported\; }\tilde{X}\left(k\right)\cdot \text{W}{}_{\text{N}}^{-\text{k}\text{n}}$

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