The following is the relationship between the relevant angles and edges:
• Angle ACE = angle ECD = 1⁄2 angle ACD
• Angle ACO = 90o - 1⁄2 angle BAC
• Angle OCE = angle ACE - ACO
• OE = 1⁄2 line BC x tan (OCE)
• AE = OA + OE
• ED = AD -AE
• Line EDF = 1⁄2 line BDC
• EF = sin (EDF) x ED
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