Help with this problem please

**Problem:**

1) __Both__ and is always greater than zero. Are there any restictions needed on for this to be true?

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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) ?**