It is given that
PSSQ=PTTR
So, ST || QR [By converse of Basic Proportionality Theorem] (1 Mark)
∴∠PST=∠PQR
(Corresponding Angles) (1 Mark)
Also, it is given that
∠PST = ∠PRQ
So, ∠PRQ = ∠PQR
Therefore, PQ = PR (Sides opposite the equal angles)
i.e., ΔPQR is an isosceles triangle. (1 Mark)