Answer:
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in triangle PQR,
PQ=PR [Given]
= angle PRQ=angle PQR[angle opposite to the equal sides are equal]......(1)
since ST|| QR and PQ is a transversal,then
angle PQR = angle PST (corresponding angles).....(2)
since PQ || QR and PR is a transversal,then
angle PRQ=angle PST (corresponding angles).....(3)
but angle PQR = angle PRQ , then from (2) and (3) we get
angle PST = angle PTS
In triangle PST
angle PST = angle PTS (proved)
So, PT = PS (sides opposite to equal angles are equal)
Or in shorter terms,
In traingle PSR And PTS
PQ=PR (given)
RS=PT (given)
Angle A is common
So,traingles are congruent(SAS) .
So corresponding sides QT=RS