Convolution 

Frequency

(1.1)

Insert the time domains of both of these

(1.2)

Evaluate the sum on n first noting that

Delta Functions.htm -- .doc

(1.3)

To drive the point home

      (1.4)

Or

time

(1.5)

Insert the frequency domains of both of these

(1.6)

Evaluate the sum on n first (1.7)

Then note that

Delta Functions.htm .doc

So that

(1.8)

Evaluate the sum over k function to find

(1.9)

To drive the point home

(1.10)

Or

        (1.11)