I use matrices
Thanks but im wondering actually how many normal equations am i supposed to find?
Because the way we do it, is we find the error sum of squares of the model and then differentiate it wrt each of the terms i.e. etc.
so so far i have 9 normal equations, but I'm wondering if for the interaction term
which now i realise i didnt put into my question, (and i will after this post) do i differentiate it with respect to etc. ??
please help?