Given:RectangleABCDwithcenterOToProve:OB2+OD2=OC2+OA2ThroughO,drawPQ∥BCsothatPliesonABandQliesonDC.Now,PQ∥BCTherefore,PQ⊥ABandPQ⊥DC[∠B=90and∠C=90)So,∠BPQ=90and∠CQP=90Therefore,BPQCandAPQDarebothrectangles.Now,fromRightangledtriangle△OPB,OB2=BP2+OP2...(1)Similarly,fromRightangledtriangle△ODQ,OD2=OQ2+DQ2...(2)FromOPA,wehaveOA2=AP2+OP2...(3)From△OQCCQ2+OQ2=OC2Adding(1)nd(2)OB2+OD2=BP2+OP2+OQ2+DQ2=CQ2+OP2+OQ2+AP2[AsBP=CQandDQ=AP]=CQ2+OQ2+OP2+AP2=OC2+OA2[From(3)and(4))]HenceProved