Need help with communication system problem

[vptran84]

Ok, so i just started taking a course in Communication systems. So far I am confused. I am never going into communication systems, but i still have to take the required course. I'm going into either Power or Control Systems.

But anyways, I really need help with this communcation problem:

Consider a sinusoidal process with random phase, defined by
X(t)=20cos(40,000,000*pi + theta) where theta is a random variable uniformly distributed over the interval [-2p, 0).

a) What is the Mean of the process X(t): I know that the mean is u = E[X(t)]

b) What is the Autocorrelation function of X(t): I know that the autocorrelation is Rx(tau) = E[X(t+tau)X(t)].

If anyone can give me any hints, i would greatly appreciate it. thank you

 

[anorlunda]

I think it is a trick question. Changing the phase does not influence the mean or the autocorrelation.