Geometry Practice Test 5

∠ ECD = 70°
∠BDO = 20°
EC || AB
CD is a transversal line
∠ECD = ∠AOD = 70°
∠AOD = 70°
AOD+BOD = 180° (Linear pair)
∠BOD = 180° − 70° = 110°
In Δ BOD,
∠BDO+∠BOD+∠OBD = 180°
20° +110° +∠OBD = 180°
∠OBD = 180° − (20° +110°)
= 180° −130° = 50°