1. Quadrilateral ABCD is a parallelogram Given
2. AB||DC and AD||BC Opposite sides of a parallelogram are parallel.
3. <A and <B are same side interior angles Definition of a parallelogram.
<B and < C are same side interior angles
4) m <A + m<B = 180 degrees Same side angles of a parallelogram are of 180°
m<B + m<C = 180 degrees.
5) <A and <B are supplementary
<B and <C are supplementary Definition of supplementary angles.
