I taught middle school math and I'm somewhat familiar with transformations, but I have no idea what the notations in this problem mean. I looked in two geometry books with no luck. Google, no luck. Khan Academy, well, you get the idea. I'm tutoring two students who are doing distance learning, and I don't have access to their materials. I don't mind admitting that I don't know something, but I hate to look REALLY stupid.

I meet with them tomorrow.

rsn