1. The problem statement, all variables and given/known data a) find if the system is causal. b) find the impulse response given: y(t)=x(t-1)u(t) ans: a) Causal b) delta(t-1) 2. Relevant equations 3. The attempt at a solution a) I thought this is a non-causal system because if our input is delta(t), the resultant output is delta(t-1) if t=1, input value depends on delta(1), and its output is delta(0). output depends on future value. b) I don't know where that u(t) comes from... thanks.