(d) X() exp[-2π(f²-10)] 1.8. Find the autocorrelation function of x(t) = A cos (2πfot + b) in terms of its period, To=1/fo. Find the average normalized power of x(t), using P₁ = R(0). 1.9. (a) Use the results of Problem 1.8 to find the autocorrelation function R(T) of wave- form x(t) = 10 cos 10t+ 20 cos 20. (b) Use the relationship P, R(0) to find the average normalized power in x(t). Compare the answer with the answers to Problems 1.4 and 1.5.