Q4 of 100 Page 17

ABCD is a cyclic quadrilateral such that ∠ADB =30° and ∠DCA =80°, then ∠DAB =

ABCD is a cyclic quadrilateral

∠ADB = 30°


∠DCA = 80°


∠ADB = ∠ACB = 30° (Angle on the same segment)


Now,


∠BCD = ∠ACB + ∠DCA


= 30° + 80°


= 110°


∠OAB + ∠BCD = 180°


∠OAB + 110° = 180°


∠OAB = 70°

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