Join OE. In ΔOME and ΔONE, OM =ON [equal chords are equidistant from the centre] ∠OME = ∠ONE = 90° OE =OE [common sides] ∠OME ≅ ∠ONE [by SAS congruency] ⇒ ME = NE [by CPCT] In quadrilateral OMEN, ∠MON = 360° - (∠OME + ∠MEN + ∠ONE) = 360° - (90° + 90° + 90°) = 90° [∠MEN = 90°, given] Thus, in quadrilateral OMEN, OM =ON , ME = NE and ∠OME = ∠ONE = ∠MEN = ∠MON = 90° Hence, OMEN is a square. Hence proved.