It's been a while since I took Calc 2 and I am in a Linear Systems and Signals class right now. I'm looking at a solution on how to obtain a zero state response of a discrete time signal, but performing the summation confuses me. Can someone explain the steps they did? This is part A http://imageshack.us/photo/my-images/684/partal.jpg/ This is part B http://imageshack.us/photo/my-images/11/part2sy.jpg/ In Part A, where did the +1 come from? Also, how would you simplify the first fraction appearing after the equal sign of Ystep? In Part B, where did the -1 's come from? Originally, h[m] was just (6/5)[itex]\sum[/itex](-1/2)m + (24/5)Ʃ(1/3)m I have a Final next week on this stuff so, any help would be appreciated.