Solution:
According to the given question,
Since,
As a result,
….(i)
Also,
….(ii)[as we know, sides opposite to equal angles are also equal]
From eq. (i) and eq. (ii).
⇒ ST || QR
If a line is drawn parallel to triangle’s one side to intersect the other two sides in distinct points, then the other two sides are also divided in the same ratio according to the converse of basic proportionality theorem.
And
In triangles PTS and PRQ.
[Common angles]
(proved)
(proved)
[By AAA similarity criteria]
As a result, proved.