In Fig. 16.184, if ∠BAC=60° and ∠BCA=20°, find ∠ADC.
By using angle sum property in triangle ABC,
∠B = 180o – (60o + 20o)
= 100o
In cyclic quadrilateral ABCD, we have
∠B + ∠D = 180o
∠D = 180o – 100o