1. The problem statement, all variables and given/known data y(n)=x(4n+1). Is this system T.I or NOT T.I The professor marked this question wrong for my homework. He says it's NOT time invariant. I proved it is time invariant. 2. Relevant equations System is time invariant if a shift in time in input results in the same shift in time when the output is shifted. 3. The attempt at a solution shift in the x: y1=x(4(n-n0)+1) y2=shift in y=y(n-n0)=x(4(n-n0)+1) They are the same, therefore they system is time invariant. The professor marked this problem wrong for me, and he gave me the run-around when I asked for him to prove it. Did I do this right?