PQRS is a trapezium with PQ y SR. If M and N are two points on the non-parallel sides PS and QR respectively, such that MN is parallel to PQ, then show that

Join PR
PQSR and MNPQ ⇒ MNSR

In PSR, by Basic proportionality theorem, we have
...(i)
Similarly, In PQR,
...(ii)
From (i) and (ii),