Solution :- Let AC and BD bisect each other at point 0. Then, OA = OC and OB = OD In triangles AOB and COD, we have OA = OC OB = OD and ∠ AOB = ∠ COD (Vertically opposite angles) ∴ △ AOB ≅ △ COD (SAS congruence criterion) => AB = CD (CPCT) => arc AB ≅ arc CD ...(ii) Similarly BC = DA => arc BC ≅ arcDA ..(iii) From (ii) and (iii), we have arcAB + arcBC ≅ arc CD + arcDA => => arcABC = arcCDA => AC divides the circle into two equal parts. => AC is the diameter of the circle. Similarly, we can prove that BD is also a diameter of the circle. Since AC and BD are diameters of the circle. ∴ ∠ABC = 90° = ∠ADC Also, ∠BAD = 90° = ∠BCD Also, AB = CD and BC = DA (Proved above) Hence, ABCD is a rectangle.