stuck on how to go about with this problem
so I guess I need to show PQR or PQS is 90 deg.
In triangles PQR and PSQ,
RQ = QS (Q is the midpoint of RS)
PQ is common
Hence, triangles PQR and PSQ are congruent (SAS)
(corresponding angles in congruent triangles are equal)
180 degrees = (angle sum of straight equals 180 degrees)
Therefore, = 90 degrees
Hence, PQ is perpendicular to RS.