Question 1:
linear system: y = x1(2t) + x1(t)
nonlinear: y = (x(t)) • (x(t-1))
causal: y = et+5x(t-1)
noncausal: y = et-5x(t+1)
with memory: y = (x[n-5])^3
memoryless: y = (x[n]) ^ 3
invertible: y(t) = (x(t)) ^ t
uninvertible: y(t) = (sum) k=0 -> 5 kx[n]
