In the diagram given, angle PQS and angle SQR both form a linear pair. Both angles lie on a straight line. The measure of the angle of a straight line equals 180°. So therefore, two angles of a linear pair will sum up to 180°.
According to the linear pair postulate, <PQS and <SQR are supplementary, since they form a linear pair.
Therefore, the reason for statement 2 for the two-column proof is "Linear Pair Postulate".
