Given:TrapeziumABCDwithAB∥DCandAD=BC.P,Q,R,Sarerespectivelythemidpointsof BA,BD,CD and CA.ToProve:PQRSisarhombusProof:In△BDC,QandRarethemidpointsof BDandCD respectively∴QR∥BC andQR=12BC[AccordingtoMidpointTheorem]In△ABC,PandSaremidpointsofBAandACrespectively∴PS∥BCandPS=12BC(AccordingtoMidpointTheorem)Thus,PS∥QRandPS=QR[Eachequalto 12BC]∴PQRSisaparallelogram.In△ACD,SandRarethemidpointsofACandCD respectively.SR∥ADandSR=12AD=12BC[∵AD=BC(Given)]In△ABD,PandQarethemidpointsofABandBD respectively.PQ∥ADandPQ=12AD=12BC[∵AD=BC(Given)]∴PS=QR=SR=PQ.Hence,PQRSisarhombus.