Determine whether the following discrete-time systems are causal or noncausal, have memory or are memoryless, are linear or nonlinear, are time invariant or time varying. In the following parts, x[n] is an arbitrary input and y[n] is the response
to x[n].
(a) y[n] == x[n] + 2x[n - 2]
(b) y[n] == x[n] + 2x[n + 1]
(c) y[n] == nx[n]
(d) y[n] == u[n]x[n]
(e) y[n] == |x[n]|
(f) y[n] == sin x[n]
(g) y[n] == sigma (O.5)^n x[i] , n greater or equal to 0