△ABD∼△PQS and AD and PS are the medians, then
ACBC=PRQR
If △ADB∼△PSQ ,
ABPQ=ADPS=BDQS
(corresponding sides of similar triangles will be in same ratio)
∠B=∠Q (corresponding angles of similar triangles will be equal)
⇒ABPQ=2BD2QS=BCQR
Now, consider △ABC and △PQR.
∠B=∠Q
⇒ABPQ=BCQR
∴△ABC∼△PQR (by SAS similarity criterion)
ACPR=BCQR=ABPQ
⇒ACBC=PRQR