Given two random signals X1(t) = 3 cos(120t+) and X2(t) = 4 cos(120t+ ), where U(, ) and U(0, /2) are independent.

(a) Find the mean functions of X1(t) and X2(t), respectively.

(b) Find the autocorrelation functions and average powers of X1(t) and X2(t), respectively.

(c) Are X1(t) and X2(t) wide-sense stationary, respectively?

(d) Are X1(t) and X2(t) jointly wide-sense stationary?

(e) Are X1(t) and X2(t) orthogonal?