Need help with some basic math/exponential rules I don't understand. How do I get from a to be here? 
See image. I've looked up just about every rule I can find and I can't figure out how I am supposed to arrive at that answer. Can someone explain to me what has been done step by step here?

$$0.5=\frac12$$
$$0.5-1=-0.5$$
$$x^{-n}=\frac1{x^n}$$
That should be enough to figure it out
