A. What is the variance of Y_t as a function of â and t?

B. What is ñ(y_t,y_t-k) as a function of â, k, and t?

See equations 5.1.4 and 5.1.5 on page 89.

{Note: This homework assignment has been replaced because of an unclear equation in the textbook; see the new homework assignment. If you have submitted this assignment already, you will be given credit.}

I'm have the same sign error as previously posted. I get o^2e(1+b^2+b^4+...+b^(2(t-1))+0), then using the geometric formula i get o^2e[(1-b^2t)/(1-b^2)] This times -1 gives you the correct answer...but I can't figure out where the -1 is coming from. I looked at the post that said something like...subtract the rest of the series from the infinite series...1/(1-b^2)...but how do I know what the rest of the series is...isn't that also an infinite series?