BC is a diameter of a circle with center at O. If ∠ABO=30∘ and ∠OAD=40∘, find the measure of ∠COD.
+37146 Extand line AO to the other side of the circle DAO then intercept 80 degrees of a half circle
angle b intercepts anothe 60 degrees of this half cirlcle
angle cod is a central angle and intercepts the rest of the half circle 180 - 80 - 60 = 40 degrees
