This is mathematics, not English. So as a chemist I dare reply to this thread.

As stated above, the minus sign indeed means that it is part of the denominator of the fraction, and here is why:

Let's do some simple exponentiation:

2[SUP]1[/SUP] = 2

2[SUP]2[/SUP] = 4

2[SUP]3[/SUP] = 8

2[SUP]4[/SUP] = 16

You see that every time you add 1 to the exponent, the outcome doubles (exponentiation works like that). But you can also see it the other way around: every time you subtract one from the exponent, you divide by two. So we can do what we just did, but then in reversed order:

2[SUP]3[/SUP] = 8

2[SUP]2[/SUP] = 4

2[SUP]1[/SUP] = 2

but we don't have to stop here, we can simply keep dividing by 2, so:

2[SUP]0[/SUP] = 1

2[SUP]-1[/SUP] = 1/2

2[SUP]-2[/SUP] = 1/4

2[SUP]-3[/SUP] = 1/8

So what do we see? If you have a negative exponent, it's basically 1 divided by the outcome of the positive exponent (2[SUP]1[/SUP]= 2 and 2[SUP]-1[/SUP]= 1/2).

1/2 (2[SUP]-1[/SUP]) is called the mathematical inverse of 2. The reason is that dividing by 2, is the same thing as multiplying by 1/2 (and vice versa). It also works with symbols: multiplying with s[SUP]-1[/SUP] , is the same thing as dividing by s. Scientists use this a lot, because it allows you to neatly write entire fractions in just one line. Instead of meter per second m/s, they write: m s[SUP]-1[/SUP] = m * 1/s = m/s

I hope this is clear, otherwise, ask away.