Oh yes, this is from the Geometry Homework on AoPS.
I can't tell you the answer but...
Are there any triangles you can use?
Smart triangles? like 30-60-90?
Is it a coincidence that \(AB=\sqrt3\)? Maybe it's part of a 30-60-90 triangle.
You should be able to find \(DR\) with these hints.
You are very welcome!
:P