The Total solution for NCERT class 6-12
In ∆BOC and ∆AOD, we have∠BOC = ∠AODBC = AD [Given]∠BOC = ∠AOD [Vertically opposite angles]∴ ∆OBC ≅ ∆OAD [By AAS congruency]⇒ OB =OA [By C.P.C.T.]i.e., O is the mid-point of AB.Thus, CD bisects AB.