Here's a diagram to help you understand better:
-------------------------------
| P T |
| |\ /| |
| | \ / | |
| | \ / | |
| | R | |
| | / \ | |
| | / \ | |
| |/ \| |
| Q S |
--------------------------------
Let R be the point of intersection of QT and PS.
Since QT bisects PS as given, then PR = RS.
Since every line has a total angle sum of 180°, then:
m/_SRT = 180° - m/_PRT = 180° - (180° - m/_PRQ) = m/_PRQ.
However, write in your proof: m/_SRT = m/_PRQ by vertical angles.
Since PQ || ST as given, then m/_QPS = m/_PST,
also since they are alternate interior angles.
Therefore, by ASA (angle side angle), /_\PQR = /_\RST.
Finally, PQ = ST, due to CPCTC
(corresponding parts of congruent triangles are congruent).
Arsene2006 M.
This didn’t work11/12/20