Question

In following figure.,ABCD is a cyclic quadrilateral . If ∠ BCD = 100° and ∠ ABD = 70° , find ∠ ADB.

Answer 1

In cyclic quadrilateral ABCD, 

∠ BCD + ∠ DAB = 180°  (Opposite angles of a cyclic quadrilateral)

100 + ∠ DAB = 180

∠ DAB = 80°

In Δ DAB ,

∠ DAB + ∠ ABD + ∠ BDA = 180°

80 + 70° + ∠ BDA = 180°

∠ BDA = 30°