Digging out the old textbook

I got a phone call from an old friend last night, who remembered my long-ago days as a math whiz and wanted some help with this problem:

If you are standing at a point in the woods, and you project out two lines of known length in two separate compass directions, then how can you determine the compass direction of a line that connects the end points of the two lines you've projected?

So I sat down and spent half an hour solving my first trig problem in 11 years. It was fun. I don't do that sort of thing often enough any more.