6(a)

The definition of time-invariant is

If the cascade

x(t)--->[time delay by t0]----->[system]-----z(t) ---(1)

yields the same output as the reverse of (a);x(t)--->[system]--->[time delay by t0]---y(t), it is called Time invariant.

When I substitute into (1) and the reverse order of (1), the results are not the same. Thus, it is not time-invariant.

6(b)

Assuming that this is linear. X[n]=&delta[n-1]

we make the output Y[n]=u[n-1]. To get this result, the input would be X[n]=u[n].

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Abstract algebra continues the conceptual developments of linear algebra, on an even grander scale.

Dr. Paul Garrett