Well, there could be so many derived formulas....the ones previously mentioned, radial to arc, arc to radial, it became second nature. All now lost, as in elementary school my grandson now uses a calculator for what had to become 2nd nature for us...the times tables,etc. Progress? We old fogies know it could be done, and could be 2nd nature. We marvelled at guys being able to do Adcock Range approaches, and even more 'basic' approaches, before 'our time'.. That we didn't have to do them with oh so modern ADF-DME-VOR-Loran-Starshots, just means time marched on, I guess. And it continues, and nothing really changes.