ABCD is a cyclic quadrilateral. Side AB is extended beyond B to a point E, and $\angle CBE = 78^\circ$. What is $\angle ADC$?

Explanation

1. 01

   $\angle ABC = 180^\circ - 78^\circ = 102^\circ$ (angles on the straight line AE).

2. 02

   Opposite angles of a cyclic quadrilateral are supplementary: $\angle ADC = 180^\circ - 102^\circ = 78^\circ$.