1) Both and is always greater than zero. Are there any restictions needed on for this to be true?
EDIT (21 OCT 07):
Let me clarify what my actual question is. Sorry for not making this clear enough early on.
The question I am asking is this:
1) What restrictions (i.e. the general rule) are needed on and so that there are some range of values of and to make both and positive?
2) What is the restriction (i.e. the general rule) for and such that no matter what combination of and is chosen (but still sums to 100), and is always negative?
3) How can you prove your answers to questions 1) and 2) ?