Please correct statements and answer questions below:
1) So to go from STEP 1 to STEP 2, the limits of the series are changed from -infinity, + infinity to 0,+ infinity because u[n] is 1 for n>=0 and 0 otherwise. Correct?
2) In STEP 2 we substitute the value of x[n] so the term u[n] is not found in STEP 2 because it is evaluated as 1. Correct?
3) If term u[n] is no longer in STEP 2 equation how can we use the transform equation (indicated by arrow) in table when only (1/2)^2 remains?
If you have a different explanation on how to transition from STEP 1 to STEP 3. Please feel free to comment.