Ok, so this review packet I am working from does not fully explain their answers, and I am having difficulty following some of them. Any help would be greatly appreciated.

Here is the expression:

(x^-1 – y^-1) / (x-y)^-1

Now, I understand the next step:

(1/x - 1/y) / (1/x-y)

But how do they get to this:

(x-y)(y-x)/xy

I tried working backwards, but I guess mu understanding of fractions is a bit rusty. Am I supposed to multiply by (1/x-y)? What is the best way to approach a problem like this? Thanks in advance.