An inscribed angle is measured by one-half its intercepted arc. Inscribed angle ∠CAD and ∠DBC both subtend the same arc CD. So ∠CAD = ∠DBC = 30° That means ∠BAD = ∠BAC + ∠CAD = 50° + 30° = 80° Since inscribed angle ∠BAD is measured by one-half its intercepted arc, its intercepted arc BCD = 2(80°) = 160°. arc BCD + arc BAD = 360°, 160° + arc BAD = 360°, arc BAD = 200° inscribed angle ∠BCD = 100° since it subtends arc BAD, and has the measure of one-half its intercepted arc. Edwin