The Total solution for NCERT class 6-12
Let ABCD be a cyclicquadrilateral having diagonals BD and AC, intersecting each other at point O.
(Consider BD as achord)
∠BCD+ ∠BAD = 180° (Cyclic quadrilateral)
∠BCD= 180° − 90° = 90°
(Considering AC as achord)
∠ADC+ ∠ABC = 180° (Cyclic quadrilateral)
90° + ∠ABC= 180°
∠ABC= 90°