A finite duration discrete-time signal $x[n]$ is obtained by sampling the continuous-time signal $x\left ( t \right )=\cos\left ( 200\pi t \right )$ at sampling instants $t=n/400, n=0, 1, \dots ,7.$ The $8$-point discrete Fourier transform $\text{(DFT)}$ of $x[n]$ is defined as $$X\left [ k \right ]=\sum ^{7}_{n=0}x\left [ n \right ]e^{-j\frac{\pi kn}{4}}, k=0,1, \dots ,7.$$