Xác định kết quả biến đổi Fourier của tín hiệu y ( n ) = x ( n ) c o s ω 0 n

$Y\left(e{}^{j\omega }\right)=FT\left[x\left(n\right)\text{c}\text{o}\text{s}\omega {}_{0}n\right]=\frac{1}{2}X\left(e{}^{j\left(\omega +\omega {}_0\right)}\right)-\frac{1}{2}X\left(e{}^{j\left(\omega -\omega {}_0\right)}\right)$

$Y\left(e{}^{j\omega }\right)=FT\left[x\left(n\right)\text{c}\text{o}\text{s}\omega {}_{0}n\right]=\frac{1}{2}X\left(e{}^{j\left(\omega +\omega {}_0\right)}\right)+\frac{1}{2}X\left(e{}^{j\left(\omega -\omega {}_0\right)}\right)$

$Y\left(e{}^{j\omega }\right)=FT\left[x\left(n\right)\text{c}\text{o}\text{s}\omega {}_{0}n\right]=X\left(e{}^{j\left(\omega +\omega {}_0\right)}\right)+X\left(e{}^{j\left(\omega -\omega {}_0\right)}\right)$

$Y\left(e{}^{j\omega }\right)=FT\left[x\left(n\right)\text{c}\text{o}\text{s}\omega {}_{0}n\right]=X\left(e{}^{j\left(\omega +\omega {}_0\right)}\right)-X\left(e{}^{j\left(\omega -\omega {}_0\right)}\right)$