\frac{{\sin (\omega _c n)}}{n} \Leftrightarrow X(e^{j\omega } ) = \left\{ {\begin{array}{*{20}c} {1,\left| \omega \right| \le \omega _c } \\ {0,\omega _c < \left| \omega \right| \le \omega _c } \\ \end{array}} \right.
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