For each of the following systems, determine whether or not the system is (1) linear, (2) time-invariant, and (3) causal: a. y[n]=x[n]cos(0.2πn) b. y[n]=x[n]−x[n−1] c. y[n]=∣x[n]∣ d. y[n]=Ax[n]+B, w
here A and B are nonzero constants.