Find all of the points of the form (x, -x) which are 1 unit from the origin.

The answer is given as

(sqrt(2)/2, -sqrt(2)/2), (-sqrt(2)/2, (sqrt(2)/2)

I understand the other questions but I'm totally lost on how this answer was obtained. It's found in a chapter on If someone could work the problem so I can see how it is done, I would really appreciate it.