A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robert Bernecky
Date: 2021 Mar 3, 07:22 -0800
use the law of sines to set up 3 equations. With x = angle BAD:
sin(CAD + x) / BC = sin(ACB) / AB
sin(x) / BD = sin(ADB) / AB
sin(BCD) / BC = sin(BCD) / BD
The first two give sin(CAD + x) / sin(x) = sin(ACB) / sin(ADB) * (BC/BD). The third gives an expression for BC/BD.