S and T are points on sides PR and QR of △PQR such that ∠P = ∠RTS. Show that △RPQ ≅ △RTS.

In △RPQ and △RTS
∠R is common
∠RTS = ∠P (Given)
∠PRQ = ∠TRS = ∠R (Common)
Hence, By AA criterion of similarity, △RPQ ≅ △RTS [hence proved]