Help with DTFS
Hello. I came across this question in BP Lathi's Linear Signals and Systems book and I don't really understand it:
Obtain the period and the DTFS of x[n]=4cos[0.2*pi*n]+6sen[0.5*pi*n].
I managed to find the period correctly (N = 20 samples), but I am confused as to how to find the DTFS itself. Lathi uses the formula below:
I did rewrite the signal as complex exponentials but I was not able to write Dr as function that was not a sum. In some examples, Lathi defines the limits of the sum differently. He still keeps the total of No indexes, but doesn't start at n=0. What difference does that make?
Thank you in advance.