PSSQ = PTTR and ∠PST = ∠PRQ. Prove that Δ PQR is an isosceles triangle.
It is given that PSSQ = PTTR⋅
So, ST || QR (Theorem)
∴ ∠PST = ∠PQR (Corresponding angles) (1)
Also, it is given that
∠PST = ∠PRQ (2)
So, ∠PRQ = ∠PQR [From (1) and (2)]
∴ PQ = PR (Sides opposite the equal angles)
i.e., PQR is an isosceles triangle.