Churchill–Bernstein equation prove or history

[Doctor_Doom]

Hey guys I'm after some proofs or equation steps or historical information in regards to the Churchill–Bernstein equation (equation below).

http://img100.imageshack.us/img100/6491/01fa2369ae0e0ddbec6f69c.png

This is for a lab project so would like some theory/background on the matter.

Thanks in advance!