Any fraction of the form or is equivalent to . I'm not going to bother with a general proof, but in your case:
Every time I think I understand how to deal with a minus in a question, something different crops up. I thought I could do this but I need a little help on the last stage.
Rewrite the expression with a rational denominator.
Now what do I do to get rid of the minus on the denominator?
I know the answer is but cannot fathom how they got there.
If I multiply top and bottom by -13, don't I end up with