ABCD is a trapezium with AB parallel to DC. $\angle A = 65^\circ$ and $\angle B = 50^\circ$. What is $\angle C$?

Explanation

1. 01

   $AB \parallel DC$, and BC is a transversal, so $\angle B$ and $\angle C$ are co-interior angles: $\angle B + \angle C = 180^\circ$.

2. 02

   $\angle C = 180^\circ - 50^\circ = 130^\circ$. (Similarly $\angle D = 180^\circ - 65^\circ = 115^\circ$.)