Công thức nào sau đây là đúng:

$x\left(n\right)=\frac{1}{2j\pi }\oint X\left(Z\right)\cdot Z{}^{-n}dZ$

$x\left(n\right)={\displaystyle \sum }_{n=-\infty }\mathrm{Unsupported\; }x\left(Z\right)Z{}^{-n}$

$\text{I}\text{Z}\text{T}\left[x\left(Z\right)\right]=\frac{1}{2j\pi }\oint {}_{c}x\left(Z\right)\cdot Z{}^{n-1}dZ$

$x\left(n\right)={\displaystyle \sum }_{n=-\infty }\mathrm{Unsupported\; }x\left(Z\right)Z{}^{n-1}$