Just solve for a and d, also plot |X(jω)| using a plotting software like Python for a and d. I am having trouble with the code.
5.21. Compute the Fourier transform of each of the following signals:
(a) x[n] = u[n-2] - u[n-6]
(b) x[n] = (-n)u[-n-1]
(c) x[n] = |n|u[-n-2]
(d) x[n] = 2sin(n)u[-n]