In the figure ABCD is a cyclic quadrilateral whose side AB is a diameter of the circle through A , B , C and D. If ∠ADC = 120°, find ∠BAC. Share with your friends Share 0 Atul Shaw answered this Dear student,ABCD is cyclic quad.So, sum of opposite angles are 180∘.∠D+∠B=180∘⇒120∘+∠B=180∘⇒∠B=60∘-----(1)AB is diameter. Diameter subtends 90∘ on circumference of circle.⇒∠ACB=90∘----(2)In △ABC,∠BAC+∠CBA+∠ACB=180∘ (sum of interior angles of △)⇒90∘+60∘+∠BAC=180∘⇒∠BAC=30∘Regards 1 View Full Answer