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)
тИаBCD+ тИаBAD = 180┬░ (Cyclic quadrilateral)
тИаBCD= 180┬░ тИТ 90┬░ = 90┬░
(Considering AC as achord)
тИаADC+ тИаABC = 180┬░ (Cyclic quadrilateral)
90┬░ + тИаABC= 180┬░
тИаABC= 90┬░