The following is the relationship between the related angles and edges:

• Angle ACE = Angle ECD = ½ Angle ACD

• Angle ACO = 90º -½ Angle BAC

• Angle OCE = Angle ACE-ACO

• OE = ½ line BC x tan (OCE)

• AE = OA + OE

• ED = AD -AE

• Line EDF = ½ line BDC

• EF = sin (EDF) x ED