Re: Exercise 3.4
I'm having a bit of difficulty with 3.4b. I take \hat(y)  y and multiply by (XX^T)^{1}XX^T, which ends up reducing the expression to just H\epsilon. However, then I can't use 3.3c in simplifying 3.3c, which makes me think I did something wrong. Can somebody give me a pointer?
Also, it'd be great if there was instructions somewhere about how to post in math mode. Perhaps I just missed them?
